CSS水平垂直居中方法总结

一、已经元素宽高（1）定位布局

[code]<div class="box">
<div class="contain"></div>
</div>

[code].box{
width:200px;
height: 200px;
background: red;
margin: 0 auto;
position: relative;

}
.contain{
width: 50px;
height: 50px;
background: gray;
position: absolute;
left: 50%;
top: 50%;
margin: -25px 0 0 -25px;
}

二、已经元素宽高（2）定位布局

[code].box{
width:200px;
height: 200px;
background: red;
margin: 0 auto;
position: relative;

}
.contain{
width: 50px;
height: 50px;
background: gray;
position: absolute;
left: 50%;
top: 50%;
transform: translate(-50%,-50%)
}

三、已经元素宽高（3） flex布局

[code].box{
width:200px;
height: 200px;
background: red;
margin: 0 auto;
display: flex;
justify-content: center;
align-items: center;
}
.contain{
width: 50px;
height: 50px;
background: gray;
}

四、未知元素宽度（这种是宽度自适应）

[code].box{
width:200px;
height: 200px;
background: red;
margin: 0 auto;
position: relative;
}
.contain{
height: 50px;
background: gray;
position: absolute;
margin: auto;
left: 0;
top: 0;
right: 0;
bottom: 0;
}