In-depth study of how to use CSS positioning

Original: in-depth study of how to use CSS positioning

CSS positioning presentation #

positionProperties said in English word 位置meaning, in CSSa positioning element in a major role.
CSSThere are a 3kind of positioning is as follows:

Property Value	description
fixed	Set a fixed orientation.
relative	Set relative positioning.
absolute	Setting absolute positioning.

Fixed positioning practice #

Before we take a look at the practice of fixed positioning code structure looks like it.
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      
       width: 100px;
       height: 100px;
       background-color: red;
       margin: 0;
       padding: 0;
     }
     div{
       width: 200px;
       height: 200px;
       background-color:springgreen;
        margin: 0;
        padding: 0;
     }
  </style>
</head>

<body>
   <h1 class="box"></h1>
   <div></div>
</body>

</html>

Results Figure

Now I will h1element set to a fixed position, take a look at the structure and practice of the above What is the difference, then we analyze the characteristics of some fixed location.
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      position:fixed;
       width: 100px;
       height: 100px;
       background-color: red;
       margin: 0;
       padding: 0;
     }
     div{
       width: 200px;
       height: 200px;
       background-color:springgreen;
        margin: 0;
        padding: 0;
     }
  </style>
</head>

<body>
   <h1 class="box"></h1>
   <div></div>
</body>

</html>

Results Figure

Fixed positioning features as follows:
Fixed positioning, it is relative to the browser window to set the positioning, no matter if the page scroll, fixed positioning element position will not be affected.
Fixed positioning of elements characteristic: it is already out of the standard document flow.
Fixed positioning of elements characteristic: its level is higher than the standard elements of the document flow, so we have to h1label positioning will set up a fixed gland to the divlabel.
Fixed positioning of elements characteristic: h1labels divon the label, so the fixed positioned elements no longer take up any space.

The relative positioning of practice #

Before we look at the relative positioning of practice code structure looks like it.
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

Results Figure

Now I would classattribute value .div2element is set to relative positioning, take a look at the structure and practice of the above What is the difference, then we analyze some relative positioning features.
Block

 
 
  
  
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
       position: relative;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

Results Figure

Note: We do not set up to coordinate positions relative positioning, it will not have any movement.
Author to classattribute value of div2the element positioning coordinates practice settings.
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
       position: relative;
       left: 50px;
       top: 50px;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

Results Figure

The relative positioning of features as follows:
The relative positioning of elements which do not depart from the standard document flow.
相对定位的元素如果没有设置坐标它会在原地位置。
相对定位的元素设置了坐标位置，它会根据原来的位置开始计算移动的位置。
相对定位的元素它比标准文档流的元素层级要高，会覆盖标准文档流中的元素。
相对定位的元素它可以设置为负数。

绝对定位实践#

在实践绝对定位之前我们先看看代码结构是什么样子的呢。
代码块

 
 
  
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

结果图

现在笔者将class属性值为.div2元素设置为绝对定位，看看和上面的结构实践有什么区别，然后我们在分析一些绝对定位的特点。
代码块

 
 
  
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
       position:absolute;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

结果图

注意：绝对定位已经脱离了标准文档流。
笔者给class属性值为div2元素设置定位坐标实践，为了让读者有一个直观的印象我给最外层的div元素设置了居中对齐。
代码块

 
 
  
  Copy
  
 
 
<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      margin: 0px auto;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
       position:absolute;
       left:0px ;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

结果图

注意：绝对定位元素为什么会出现在浏览器左边缘呢，绝对定位移动原理：绝对定位的元素它会寻找父元素是否有定位，如果有定位它会根据父元素进行定位，如果父元素没有设置定位，它会在找父元素的父元素是否有定位，以此类推直到body元素就停止了，因为body元素就是浏览器的位置，说了这么多笔者给新学者一个直观的印象，那咱们就实践见真招。
代码块

 
 
  
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<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>定位</title>
  <style>
     .box{
      width: 400px;
      height: 300px;
      border:  1px solid darkorange;
      margin: 0px auto;
      position: relative;
      
     }
    .box div{
       width: 100px;
       height: 100px;
     }
     .div1{
       background-color: red;
     }
     .div2{
       background-color: slateblue;
       position:absolute;
       right:0px ;
     }
     .div3{
       background-color: springgreen;
     }
  </style>
</head>

<body>
   <div class="box">
     <div  class="div1"></div>
     <div class="div2"></div>
     <div class="div3"></div>
   </div>
</body>

</html>

结果图

注意：现在笔者给绝对定位坐标更换成了向右定位，父元素设置了一个相对定位，在这里就不多进行实践了，如果定位的父元素的父元素也就是爷爷的元素，父元素和爷爷元素同时都设置了定位，该元素会根据父元素决定定位而不是爷爷元素。
绝对定位特点分析如下：
绝对定位元素它已经脱离了标准文档流。
绝对定位元素它会覆盖掉标准文档流的元素。
绝对定位元素它已经不再占用任何空间了。
绝对定位元素它根据父元素之祖先元素之间是否有定位，如果有根据最近元素进行设置定位的位置，如果没有根据body元素进行定位。
绝对定位元素的父元素可以是用任何定位包括绝对定位，笔者建议是用相对定位，一般相对定位是配合着绝对定位使用的。

In-depth study of how to use CSS positioning

CSS positioning presentation #

Fixed positioning practice #

The relative positioning of practice #

绝对定位实践#

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