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A brief analysis of CSS marging

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Jul 21, 2016 pm 02:53 PM

1. Margin can be negative

In the box model, the width/height, padding, and border of the content area cannot be negative values, with the exception of margin, which can be negative values.

I don’t know much about the techniques for using negative margins. I will add more when I have the opportunity in the future. Here are two classic applications.

1. The negative value of margin-left is combined with floating to achieve a fluid layout that does not change the DOM structure.

(This demo is the same as the one in the CSS float analysis article.)

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 3</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 4</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="utf-8"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 5</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>不改变DOM结构的流体布局<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 6</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 7</span> <span style="background-color: #f5f5f5; color: #800000;">            .container </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;"> 8</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">600px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;"> 9</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-left</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">10</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-right</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">11</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> orange</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">12</span> <span style="background-color: #f5f5f5; color: #ff0000;">                font-size</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 16px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">13</span> <span style="background-color: #f5f5f5; color: #ff0000;">                line-height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 1.5</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">14</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">15</span> 
<span style="color: #008080;">16</span> <span style="background-color: #f5f5f5; color: #800000;">            .box1 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">17</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">100%</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">18</span> <span style="background-color: #f5f5f5; color: #ff0000;">                float</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">left</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">19</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">20</span> 
<span style="color: #008080;">21</span> <span style="background-color: #f5f5f5; color: #800000;">            .box2 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">22</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-right</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 220px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">23</span> <span style="background-color: #f5f5f5; color: #ff0000;">                padding-left</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 20px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">24</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">25</span> 
<span style="color: #008080;">26</span> <span style="background-color: #f5f5f5; color: #800000;">            img </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">27</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">200px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">28</span> <span style="background-color: #f5f5f5; color: #ff0000;">                float</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">left</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">29</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-left</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">-200px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">30</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">31</span> 
<span style="color: #008080;">32</span> <span style="background-color: #f5f5f5; color: #800000;">            .clearfix:after </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">33</span> <span style="background-color: #f5f5f5; color: #ff0000;">                content</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> ""</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">34</span> <span style="background-color: #f5f5f5; color: #ff0000;">                display</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> table</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">35</span> <span style="background-color: #f5f5f5; color: #ff0000;">                clear</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> both</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">36</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">37</span> 
<span style="color: #008080;">38</span> <span style="background-color: #f5f5f5; color: #800000;">            .clearfix </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">39</span> <span style="background-color: #f5f5f5; color: #ff0000;">                *zoom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 1</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">40</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">41</span> 
<span style="color: #008080;">42</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">43</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">44</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">45</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container clearfix"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">46</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box1"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">47</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box2"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">48</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">h3</span><span style="color: #0000ff;">></span>不改变DOM位置的流体布局<span style="color: #0000ff;"></</span><span style="color: #800000;">h3</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">49</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>假如有一段文本和一幅图像，在DOM节点中，文本在前，图像在后，怎么能把图像定位到右边呢？<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">50</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>通常的做法是，调换DOM节点中图像与文本的位置，让图像在前，文本在后，然后将图像浮动到右边即可。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">51</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>但这样改变DOM节点顺序始终不妥，还有什么更好的方法呢？<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">52</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>下面就介绍一种新的思路来完成布局。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">53</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">ul</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">54</span>                     <span style="color: #0000ff;"><</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>将文本用div包起来，定义为box1；现在的结构是一个box1和一个img。<span style="color: #0000ff;"></</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">55</span>                     <span style="color: #0000ff;"><</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>将box1宽度设为100%，左浮动；将img设置一个宽度，也左浮动，然后margin-left设为负的宽度值；此时图像就定位到文本的右边啦。<span style="color: #0000ff;"></</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">56</span>                     <span style="color: #0000ff;"><</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>但是有一个问题，图像盖住了文本内容，这可怎么办？<span style="color: #0000ff;"></</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">57</span>                     <span style="color: #0000ff;"><</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>重点来了，在box1中增加一个box2，box2把文本全部包起来，然后margin-right设为图像的宽度（+额外的间距），这样就解决问题啦！<span style="color: #0000ff;"></</span><span style="color: #800000;">li</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">58</span>                 <span style="color: #0000ff;"></</span><span style="color: #800000;">ul</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">59</span>                 <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span><span style="color: #008000;"><!--</span><span style="color: #008000;">关闭box2</span><span style="color: #008000;">--></span>
<span style="color: #008080;">60</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span><span style="color: #008000;"><!--</span><span style="color: #008000;">关闭box1</span><span style="color: #008000;">--></span>
<span style="color: #008080;">61</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">img </span><span style="color: #ff0000;">src</span><span style="color: #0000ff;">="http://imgsrc.baidu.com/forum/w%3D580/sign=0c101fe665380cd7e61ea2e59145ad14/f9a3492762d0f7032de1758a08fa513d2797c542.jpg"</span><span style="color: #ff0000;"> alt</span><span style="color: #0000ff;">="a picture"</span><span style="color: #ff0000;"> style</span><span style="color: #0000ff;">="width:200px;height:300px"</span> <span style="color: #0000ff;">/></span>
<span style="color: #008080;">62</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span><span style="color: #008000;"><!--</span><span style="color: #008000;">关闭container</span><span style="color: #008000;">--></span>
<span style="color: #008080;">63</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">64</span> <span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

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2. Negative margin values realize two-column equal-height layout

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 3</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 4</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="utf-8"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 5</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>margin负值实现等高布局<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 6</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 7</span> <span style="background-color: #f5f5f5; color: #800000;">            div.container </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;"> 8</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-left</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 200px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;"> 9</span> <span style="background-color: #f5f5f5; color: #ff0000;">                overflow</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> hidden</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">10</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">11</span> 
<span style="color: #008080;">12</span> <span style="background-color: #f5f5f5; color: #800000;">            div.box </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">13</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;">300px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">14</span> <span style="background-color: #f5f5f5; color: #ff0000;">                float</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> left</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">15</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-right</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 20px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">16</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">17</span> 
<span style="color: #008080;">18</span> <span style="background-color: #f5f5f5; color: #800000;">            div.box1 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">19</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> brown</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">20</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> -9999px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">21</span> <span style="background-color: #f5f5f5; color: #ff0000;">                padding-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 9999px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">22</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">23</span> 
<span style="color: #008080;">24</span> <span style="background-color: #f5f5f5; color: #800000;">            div.box2 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">25</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> green</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">26</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> -9999px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">27</span> <span style="background-color: #f5f5f5; color: #ff0000;">                padding-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 9999px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">28</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">29</span> 
<span style="color: #008080;">30</span> <span style="background-color: #f5f5f5; color: #800000;">            p </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">31</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 50px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">32</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">33</span> 
<span style="color: #008080;">34</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">35</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">36</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">37</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">38</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box box1"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">39</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box1<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">40</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box1<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">41</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">42</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box box2"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">43</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">44</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">45</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">46</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">47</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">48</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">49</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">50</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>box2<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">51</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">52</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">53</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">54</span> <span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

Copy after login

View Code

The implementation principle is that the negative value of margin and the positive value of padding cancel each other out.

2. The percentage value of margin

When the value of the margin attribute is a percentage, it is always calculated based on the width of the parent element.

Please take a look at the demo below, which tortured me for a long time. . . It's just that I found out too late, and it would make me cry if I talked about it too much. . .

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 3</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 4</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="utf-8"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 5</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>margin的百分数值<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 6</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 7</span> <span style="background-color: #f5f5f5; color: #800000;">            .container </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;"> 8</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 500px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;"> 9</span> <span style="background-color: #f5f5f5; color: #ff0000;">                height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 300px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">10</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 50px auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">11</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> orange</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">12</span> <span style="background-color: #f5f5f5; color: #ff0000;">                border</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 1px solid black</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">13</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">14</span> 
<span style="color: #008080;">15</span> <span style="background-color: #f5f5f5; color: #800000;">            .box </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">16</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 250px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">17</span> <span style="background-color: #f5f5f5; color: #ff0000;">                height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 150px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">18</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-left</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">19</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-right</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">20</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> cyan</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">21</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">22</span> 
<span style="color: #008080;">23</span> <span style="background-color: #f5f5f5; color: #800000;">            .box1 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">24</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-top</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 75px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">25</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 75px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">26</span> <span style="background-color: #f5f5f5; color: #ff0000;">                padding</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 5px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">27</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">28</span>             
<span style="color: #008080;">29</span> <span style="background-color: #f5f5f5; color: #800000;">            .box2 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">30</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-top</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 25%</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">31</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 25%</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">32</span> <span style="background-color: #f5f5f5; color: #ff0000;">                padding</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 5px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">33</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">34</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">35</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">36</span> 
<span style="color: #008080;">37</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">38</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">39</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box box1"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">40</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>父元素的高度为300px，子元素的高度为150px，只要margin-top和margin-bottom都为75px，这个盒子就能垂直居中。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">41</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>OK，居中啦！！！<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">42</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">43</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">44</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">45</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box box2"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">46</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>既然子元素的高度是父元素高度的50%，那么只要margin-top和margin-bottom都为25%，应该也能垂直居中。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">47</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>额，这什么鬼？说好的居中呢？<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">48</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">49</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">50</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">51</span> <span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

Copy after login

View Code

3. Merging of margins in the vertical direction

This problem often causes some confusion, but you only need to remember one sentence. Margins in the vertical direction will be merged as long as there is close contact, and only close contact will be merged.

The merging of margins in the vertical direction is actually easy to understand if it occurs on adjacent elements; but if it occurs between a parent element and a child element, it is a little weird.

Let’s look at an example:

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 3</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 4</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="utf-8"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 5</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>垂直方向上的margin合并<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 6</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 7</span> <span style="background-color: #f5f5f5; color: #800000;">            .container </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;"> 8</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 500px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;"> 9</span> <span style="background-color: #f5f5f5; color: #ff0000;">                height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 300px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">10</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 50px auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">11</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> orange</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">12</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">13</span> 
<span style="color: #008080;">14</span> <span style="background-color: #f5f5f5; color: #800000;">            .box </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">15</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 300px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">16</span> <span style="background-color: #f5f5f5; color: #ff0000;">                height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 200px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">17</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-left</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">18</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-right</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">19</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> cyan</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">20</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-top</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 25px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">21</span> <span style="background-color: #f5f5f5; color: #ff0000;">                padding</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 5px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">22</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">23</span> 
<span style="color: #008080;">24</span> <span style="background-color: #f5f5f5; color: #800000;">            .border </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">25</span> <span style="background-color: #f5f5f5; color: #ff0000;">                border</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 1px solid black</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">26</span>                 <span style="background-color: #f5f5f5; color: #008000;">/*</span><span style="background-color: #f5f5f5; color: #008000;">padding: 1px;</span><span style="background-color: #f5f5f5; color: #008000;">*/</span>
<span style="color: #008080;">27</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">28</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">29</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">30</span> 
<span style="color: #008080;">31</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">32</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">33</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">34</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>父元素的margin-top为50px，子元素的margin-top为25px；<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">35</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>咦，子元素的margin-top呢？为什么都顶到父元素上边界了？<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">36</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>额，因为父元素与子元素的margin-top亲密接触了呀，所以它们合并在一起了啊。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">37</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">38</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">39</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="container border"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">40</span>             <span style="color: #0000ff;"><</span><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="box"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">41</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>可是我就是想让子元素距离父元素的上边界25px啊，我不想让它们合并呀。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">42</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>很简单，给父元素加个边框，它们就无法亲密接触了，就不会合并了啊。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">43</span>                 <span style="color: #0000ff;"><</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>或者给父元素设置padding也是可以的喔。<span style="color: #0000ff;"></</span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">44</span>             <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">45</span>         <span style="color: #0000ff;"></</span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">46</span>     <span style="color: #0000ff;"></</span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span>
<span style="color: #008080;">47</span> <span style="color: #0000ff;"></</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>

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Methods to eliminate margin merging in the vertical direction: Add border or padding to the parent element to break the close contact between the margin of the parent element and the child element.

Margin merging rules:

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><!</span><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><</span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 3</span>     <span style="color: #0000ff;"><</span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 4</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="utf-8"</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 5</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>margin合并规则<span style="color: #0000ff;"></</span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 6</span>         <span style="color: #0000ff;"><</span><span style="color: #800000;">style</span><span style="color: #0000ff;">></span>
<span style="color: #008080;"> 7</span> <span style="background-color: #f5f5f5; color: #800000;">            .container </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;"> 8</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 300px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;"> 9</span> <span style="background-color: #f5f5f5; color: #ff0000;">                height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 500px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">10</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 50px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">11</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> orange</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">12</span> <span style="background-color: #f5f5f5; color: #ff0000;">                float</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> left</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">13</span> <span style="background-color: #f5f5f5; color: #ff0000;">                border</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 1px solid black</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">14</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">15</span> 
<span style="color: #008080;">16</span> <span style="background-color: #f5f5f5; color: #800000;">            .box1,.box2,.box3,
</span><span style="color: #008080;">17</span> <span style="background-color: #f5f5f5; color: #800000;">            .box4,.box5,.box6 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">18</span> <span style="background-color: #f5f5f5; color: #ff0000;">                width</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 200px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">19</span> <span style="background-color: #f5f5f5; color: #ff0000;">                height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 150px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">20</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 30px auto</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">21</span> <span style="background-color: #f5f5f5; color: #ff0000;">                background-color</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> cyan</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">22</span> <span style="background-color: #f5f5f5; color: #ff0000;">                text-align</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> center</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">23</span> <span style="background-color: #f5f5f5; color: #ff0000;">                line-height</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 150px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">24</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">25</span> 
<span style="color: #008080;">26</span> <span style="background-color: #f5f5f5; color: #800000;">            .box1 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">27</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 30px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">28</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">29</span> 
<span style="color: #008080;">30</span> <span style="background-color: #f5f5f5; color: #800000;">            .box2 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">31</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-top</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 20px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">32</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">33</span> 
<span style="color: #008080;">34</span> <span style="background-color: #f5f5f5; color: #800000;">            .box3 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">35</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-bottom</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #0000ff;"> 30px</span><span style="background-color: #f5f5f5; color: #000000;">;</span>
<span style="color: #008080;">36</span>             <span style="background-color: #f5f5f5; color: #000000;">}</span>
<span style="color: #008080;">37</span> 
<span style="color: #008080;">38</span> <span style="background-color: #f5f5f5; color: #800000;">            .box4 </span><span style="background-color: #f5f5f5; color: #000000;">{</span>
<span style="color: #008080;">39</span> <span style="background-color: #f5f5f5; color: #ff0000;">                margin-top</span><span style="background-color: #f5f5f5; color: #000000;">:</span><span style="background-color: #f5f5f5; color: #00"></span>

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