What is the usage of relative in css
In CSS, the usage of relative is "position: relative". Relative represents relative positioning. If an element is relatively positioned, it will appear at its location; you can set the vertical or horizontal position to move the element "relative to" its starting point.
The operating environment of this tutorial: Windows 7 system, CSS3&&HTML5 version, Dell G3 computer.
First of all, let’s take a brief look at the concept of relative positioning
According to the definition on W3C, we can know that relative positioning is a very easy concept to grasp. If an element is positioned relatively, it will appear where it is. You can then move the element "relative to" its origin by setting a vertical or horizontal position.
In short, the element box set to relative positioning will be offset by a certain distance. The element retains its unpositioned shape and the space it originally occupied.
After reading the concept of css relative (relative) positioning, let’s talk about the usage of relative in detail
We all use relative positioning in css like this ：position:relative;
Example:
<html>
<head>
<style type="text/css">
h2.pos_left {
position: relative;
left: -20px;
}
h2.pos_right {
position: relative;
left: 20px;
}
</style>
</head>
<body>
<h2 id="这是位于正常位置的标题">这是位于正常位置的标题</h2>
<h2 id="这个标题相对于其正常位置向左移动">这个标题相对于其正常位置向左移动</h2>
<h2 id="这个标题相对于其正常位置向右移动">这个标题相对于其正常位置向右移动</h2>
</body>
</html>Effect:
After reading the above examples, we roughly know that relative A simple usage of positioning, let’s take a look at other uses of relative positioning.
The restrictive effect of relative on absolute
We know that absolute positions the first ancestor element whose positioning attribute is not a static attribute. If there is no relative or fixed positioning, give absolute Adding top/left, right/bottom and other attributes can cause offset, but if position: relative is added to the parent element, the absolute offset ability is limited by the parent element.
relative’s limiting effect on overflow
Let’s look at an example:
<html>
<head>
<style type="text/css">
.box {
overflow: hidden;
width: 50px;
height: 50px;
background-color: #dddddd;
}
.son {
position: absolute;
width: 100px;
height: 100px;
background-color: #cd0000;
}
</style>
</head>
<body>
<div class="box">
<div class="son"></div>
</div>
<div class="box" style="position: relative">
<div class="son"></div>
</div>
</body>
</html>Effect:
In this In the example, the width and height of .box are both 50px, while the width and height of the .son element are both 100px. Although the .box element has overflow:hidden set, it still cannot limit the size of the .son element. Its width and height are both is 100px, and when .box sets the positioning attribute relative, the width and height of the .son element become 50px.
relative’s limiting effect on hierarchical z-index
The two absolutes in the page have different z-indexes and have their own levels. When the parent classes of these two absolutes have relative At this time, their level depends on the relative z-index of the parent class.
The above is the entire content of this article. For more details about CSS relative positioning, you can follow the CSS video tutorial for further learning.
Recommended learning: css video tutorial
The above is the detailed content of What is the usage of relative in css. For more information, please follow other related articles on the PHP Chinese website!
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