Share six methods of vertical and horizontal centering in CSS

Summarizes several ways to achieve CSS centering. Note: * is the common way, "wrap" is the container, and "div" is the element to be centered.

*1.Absolute positioning, the following code can be implemented when the width and height are known, or you can use negative margins;

.div { 
    width: 200px;
    height: 200px;
    margin: auto; 
    position: absolute; 
    top: 0; left: 0; bottom: 0; right: 0; 
}

2. Without knowing the width and height of the element, just realize that a certain div is 1/2 of its parent, centered horizontally and vertically, and enlarged or reduced in proportion to the size of the parent element.

.div{
    position: absolute;
    left: 30%;
    right:30%;
    top: 25%;
    bottom:25%;
}

*3.translate, when the width is known and the height is unknown

.wrap{
    width:200px;//也可以不写，默认占总宽度的50%
    position: absolute;
    top:50%;
    left:50%;
    transform: translate(-50%,-50%);
    -webkit-transform: translate(-50%,-50%);
}

4.table-cell, when the height of the div itself is unknown and only vertical centering is achieved, ps, this In this case, the div width is 100%

.wrap{//外层容器
    display: table;
}
.div{//内层容器
    display: table-cell; 
    vertical-align: middle; 
}

*5.flex layout. If the width is not fixed, just set display:flex in the parent container.

.wrap{
    display: flex;
    display: -webkit-flex;
    justify-content: center;
    align-items: center;   
}

6. Hack method, good at using :after.

.wrap {  
    text-align: center; 
    overflow: auto; 
}   
.wrap:after, 
.div { 
    display: inline-block; 
    vertical-align: middle; 
}   
.div:after { 
    content: ''; 
    height: 100%; 
    margin-left: -0.25em; /* 需要根据不同的字号做调整 */ 
}   
.wrap { 
    max-width: 99%; /* 防止文档过长时会到容器的顶部 */ 
    max-width: calc(100% - 0.25em) /* Only for IE9+ */  
}

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