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There are four types of css3 positioning: 1. Relative (relative positioning), the offset reference element is the element itself, which will not cause the element to break away from the document flow; 2. Absolute (absolute positioning), the closest parent element Positioning elements are reference coordinates; 3. fixed (fixed positioning); 4. static (static positioning).
The operating environment of this tutorial: Windows 7 system, CSS3 version, Dell G3 computer.
There are four different types of css positioning. The position values are: static, relative, absolute, fixed
1. Relative (relative positioning)
relativeThe offset reference element for relative positioning is the element itself, which will not cause the element to break away from the document flow . The space occupied by the element's initial position will be retained. Relatively positioned elements are often used as parent elements of absolutely positioned elements. And positioned elements are often hierarchically graded with z-index attributes
##Code example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.rel{
width: 200px;
height:200px;
background: red;
position: relative;
top:200px;
left: 200px;
}
</style>
</head>
<body>
<p class="rel">相对定位</p>
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</body>
</html>Rendering:
##Although the rel element is biased Move, but the text does not fill its original position. It can be seen that the relatively positioned element does not break away from the document flow, and the original position will still be retained.
##2. Absolute (absolute positioning)Absolute The positioned element
takes the nearest positioned element in the parent element as the reference coordinate. If the parent element of the absolutely positioned element does not use positioning, then the reference object of the absolutely positioned element is html, elements will break out of the document flow. It's as if was deleted from the document stream. And positioned elements are often hierarchically graded with the z-index attribute
##Code example:<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.abs{
width: 200px;
height:200px;
background: red;
position: absolute;
top: 200px;
left: 200px;
}
</style>
</head>
<body>
<div>绝对定位</div>
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</body>
</html>Rendering:
Let me dispel the rumors!
takes the initial containing block as a reference. Its size is consistent with the viewport, but it is not generated by the Viewport, but by the root element . Code example:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<style>
* {
margin:0px;
padding:0px;
}
body {
height:1500px;
}
div {
width:100px;
height:100px;
background:green;
position:absolute;
bottom:0px;
}
</style>
</head>
<body>
<div></div>
</body>
</html>Instance rendering:
If the reference object is body or In the case of document, the p element must be located at the very bottom of the page. Note that there is a scroll bar here, and the element is only located at the very bottom of the viewport. 
3、
fixed ( Fixed positioning)The reference coordinate of the displacement is the visual window, and fixed elements are used to break away from the document flow. And positioned elements are often hierarchically graded with z-index attributes
Example code:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.fix{
width:200px;
height: 200px;
background: red;
position: fixed;
top: 200px;
left: 200px;
}
</style>
</head>
<body>
<div>固定定位</div>
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</body>
</html>Example Rendering:
Fixed fixed positioning and absolute positioning are similar. They can both cause displacement of elements. The above demonstrates fixed positioning; if you haven’t done so so far, To see the difference between absolute positioning, we can add more text in the text to cause the browser to generate a scroll bar. Drag the scroll bar to see the difference between the two positioning methods. Fixed positioned elements, as their name suggests, can be fixed at a certain position. Absolute positioning will move the position as the scroll bar scrolls.
4. static (static positioning)
Default value, the element box is generated normally, the offset properties of top left, bottom right will not affect its static positioning Normal display
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