Related usage of css_position_html/css_WEB-ITnose-HTML Tutorial-php.cn

Related usage of css_position_html/css_WEB-ITnose

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Release： 2016-06-24 11:38:54

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Introduction

position is used to fix the position and is a particularly important attribute

The value can be:

static: Default value, ignore top, bottom, left , right or z-index statement

relative: relative to the positioning of the parent area and the previous subset area, use top, bottom, left, right to set, you can use Z-index

absobute: Positioning relative to the position [upper left corner] of the parent area, set with top, bottom, left, right, you can use z-index

fixed: relative to the browser For positioning, ignoring other positions such as the parent position, you can use Z-index

inherit: inherit the attributes of the parent position

specifically

 1 <style type="text/css"> 2 div 3 { 4 position:100px 100px; 5 width:100px; 6 height:100px; 7 border:5px solid black; 8 } 9 div.pos_left10 {11 position:relative;12 left:-20px;13 border:5px solid green;14 }15 div.pos_right16 {17 position:relative;18 left:20px;19 border:5px solid green;20 }21 div.pos_ab22 {23 position:absolute;24 left:30px;25 top:50px;26 border:5px solid blue;27 }28 div.main29 {30 position:absolute;31 left:100px;32 top:50px;33 width:200px;34 height:300px;35 border:5px solid red;36 }37 div.pos_fix38 {39 position:fixed;40 left:10px;41 top:0px;42 clip:rect(0px 50px 200px 0px);43 }44 </style>45 </head>46 47 <body>48 <div class="main">49     <div>1.normal</div>50     <div class="pos_left">2.re-left:-20px</div>51     <div class="pos_right">3.re-left:20px</div>52     <div class="pos_ab">4.ab-(left:30px,top:50px)</div>53     <div class="pos_right">5.re-left:20px</div>54     <div class="pos_fix">6.fix-(left:30px,top:50px)</div>55 </div>

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Among them:

[2], [3], [5] are relative

When setting position: relative

, refer to the parent middle-top The upper left corner of the content area of a child element is positioned using the original point combined with the TRBL attribute. If there is no parent, the upper left corner of the BODY is used as the original point

?? It must be noted that the upper left corner relative to the previous child element is not the upper left corner shown in the 2 to 3 picture. In other words, if [2] is static, the upper left corner will not be TRBL transformed.

??That is, even if the relative element is TRBL transformed, the interval it occupies is still the original interval, so it will cover other elements.

More obvious display:

Change [2] in the picture:

position: relative;
left:-20px;
top:-50px;

Then:

An area in the figure that contains the blank areas above and below [2] and [3] is [ 2】Really occupied space

[4] is absolute

. When setting position: relative

, refer to the upper left corner of the parent The corner is positioned as the original point combined with the TRBL attribute. If there is no parent, the upper left corner of the browser is the original point

At the same time, we can see from the relative attribute [5]?? [5] is relative to the space of [3]

?? Absolute is equivalent to directly covered without possessing real space

[4] is the absolute

When setting the position: related The upper left corner is the original point

In addition

relative, absolute, and fixed are only valid when setting the TRBL attributes (TOP, RIGHT, BOTTOM, LEFT), otherwise normal HTML layout rules will be followed, and the previous object is presented immediately afterwards.

Absolute is generally not used when the page is displayed in the center, because when zooming, absolute will use the upper left corner of the browser as the vertex. Of course, it can also be fixed in a parent area and fixed width to solve the problem

clip:rect(0px 50px 200px 0px); used in [6] can crop the area

z-index, the number of layers can be set, and elements with high values will always be at low values. Above the element [Only valid when the position attribute value is absolute, relative or fixed]