Detailed explanation of css implementation of box model

This article talks about the css implementation Box Model. If you don’t know about the css implementation of the box model or are interested in the css implementation of the box model, then let’s take a look at this article together. Okay Let’s cut the nonsense and get to the point

The box model is the core basic knowledge in html+css. Only by understanding this important concept can we type better and lay out the page. The following is the knowledge I have accumulated and summarized about css box model. I hope it will be useful to beginners.

1. Concept of css box model

CSS css box model is also called box model (Box Model), including It includes several elements such as element content (content), padding (padding), border (border), and outer margin (margin). As shown in the picture:

The innermost box in the picture is the actual content of the element, that is, the element box, and the innermost box is next to the outside of the element box. The padding, followed by the border, and then the outermost layer are the margins, which form the box model. Usually the background display area we set is the range of content, padding, and borders. The outer margin is transparent and will not block other surrounding elements.

Then, the total width of the element box = the width of the element (element) + the value of the left and right margins of the padding + the values ​​of the left and right margins of the margin + the left and right margins of the border Width;

The total height of the element box = the height of the element + the value of the top and bottom margins of padding + the value of the top and bottom margins + the top and bottom width of the border.

2. CSS margin merging (overlay)

Two adjacent element boxes in the upper and lower directions meet vertically When , the margins will be merged, and the height of the merged margins is equal to the higher of the two merged margins, as shown in the figure:

is relatively easy to understand, so sometimes you need to consider this factor when encountering actual situations on the page. Of course, merging margins also has meaning, as shown below:

It should be noted that only the vertical margins of block boxes in ordinary document flow will be merged. Margins between inline boxes, floated boxes, or absolutely positioned will not be merged.

css reset is also often used

* {
  margin : 0;
  padding : 0;
}

3. box-sizing Attribute introduction

The box-sizing attribute is one of the user interface attributes. The reason why it is introduced is because this attribute is related to the box model and is included in css reset. Might use it.

box-sizing : content-box|border-box|inherit;

(1) content-box ,Default value allows the set width and height values ​​to be applied to the element's content box. The width of the box only contains the content.

　That is, the total width=margin+border+padding+width

(2) border-box, set The width value is actually the total width of border+padding+element except margin. The width of the box includes border+padding+content

　That is, the total width=margin+width

##Many CSS frameworks will calculate the box model Simplify.

(3) inherit , stipulates that the value of the box-sizing attribute should be inherited from the parent element

About border-box Usage:

1 A box width is 100%, and you want inner spacing on both sides, it is better to use it at this time

2 Global setting border-box is very good, first of all, it is intuitive , Secondly, it can save the need for addition and subtraction again and again. It also has a key function - allowing the bordered box to use the percentage width normally.

4. Applications and minor problems related to the frame model encountered in actual development.

1 Margin out of bounds (the margin-top of the first child element and the margin-bottom of the last child element are out of bounds)

以第一个子元素的margin-top 为例：

当父元素没有边框border时，设置第一个子元素的margin-top值的时候，会出现margin-top值加在父元素上的现象，解决方法有四个：

（1）给父元素加边框border （副作用）

（2）给父元素设置padding值 （副作用）

（3）父元素添加 overflow：hidden （副作用）

（4）父元素加前置内容生成。（推荐）

以第四种方法为例：

.parent {
     width : 500px;
     height : 500px;
     background-color : red;       
}.parent : before {
     content : " ";
     display : table;
}.child {
     width : 200px;
     height : 200px;
     background-color : green;
     margin-top : 50px;
}

<p class="parent">
<p class="child"></p> </p>

2 浏览器间的盒子模型。

（1）ul标签在Mozilla中默认是有padding值的，而在IE中只有margin有值。

（2）标准盒子模型与IE模型之间的差异：

　　标准的盒子模型就是上述介绍的那种，而IE模型更像是 box-sizing : border-box; 其内容宽度还包含了border和padding。解决办法就是：在html模板中加doctype声明。

3 用盒子模型画三角形

<!DOCTYPE html><html>
  <head>
    <style>
        .triangle {
            width : 0;
            height: 0;
            border : 100px solid transparent;
            border-top : 100px solid blue; /*这里可以设置border的top、bottom、left、right四个方向的三角*/
        }
    </style>
  </head>
  <body>
    <p class="triangle"></p>
  </body></html>

页面显示结果为：

以上就是本篇文章的所有内容，大家要是还不太了解的话，可以自己多实现两边就很容易掌握了哦！

相关推荐：

HTML与CSS的盒子模型

CSS布局之盒子模型属性

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