CSS设置居中的方案总结

块级元素居中 html代码部分

<div class="parent">
    <div class="child"></div>
</div>

行内元素居中 html代码部分

<div class="parent">
    <span class="child">child</span>
</div>

水平居中

01 行内元素 text-align: center;

.parent {
    text-align: center;
}

02 块级元素 margin: auto;

.parent {
    text-align: center; 
}
.child {
    width: 100px;
    margin: auto; 
    border: 1px solid blue;
}

垂直居中

01 行内元素（单行文字垂直居中）：设置 line-height = height

.parent {
   height: 200px;
   line-height: 200px;
   border: 1px solid red;
}

02 块级元素：绝对定位（需要提前知道尺寸）

缺点：需要提前知道尺寸，margin-top: -(高度的一半); margin-left: -(宽度的一半);
.parent {
    position: relative;
    height: 200px;
}
.child {
    width: 80px;
    height: 40px;
    background: blue;
    position: absolute;
    left: 50%;
    top: 50%;
    margin-top: -20px;
    margin-left: -40px;
}

03 块级元素：绝对定位 + transform

不需要提前知道尺寸
.parent {
    position: relative;
    height: 200px;
}
.child {
    width: 80px;
    height: 40px;
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    background: blue;
}

04 块级元素：绝对定位 + margin: auto;

不需要提前知道尺寸
.parent {
    position: relative;
    height: 200px;
}
.child {
    width: 80px;
    height: 40px;
    position: absolute;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    margin: auto;
    background: blue;
}

05 块级元素：padding

如果高度固定，需要提前计算尺寸（只在某些特定情况适用）
.parent {
    padding: 5% 0;
}
.child {
    padding: 10% 0;
    background: blue;
}

06 块级元素：display: table-cell

.parent {
    width: 600px;
    height: 200px;
    border: 1px solid red;
    display: table;
}
.child {
    display: table-cell;
    vertical-align: middle;
}

07 块级元素：display: flex

.parent {
    width: 600px;
    height: 200px;
    border: 1px solid red;
    display: flex;
    align-items: center;
    justify-content: center;  /*水平居中*/
}
.child {
    background: blue;
}

08 块级元素：伪元素

.parent {
    width: 300px;
    height: 300px;
    border: 1px solid red;
    text-align: center;
}
.child {
    background: blue;
    width: 100px;
    height: 40px;
    display: inline-block;
    vertical-align: middle;
}
.parent::before {
    content: '';
    height: 100%;
    display: inline-block;
    vertical-align: middle;            
}

09 块级元素：calc()

.parent {
    width: 300px;
    height: 300px;
    border: 1px solid red;
    position: relative;
}
.child {
    width: 100px;
    height: 100px;
    background: blue;
    padding: -webkit-calc((100% - 100px) / 2);
    padding: -moz-calc((100% - 100px) / 2);
    padding: -ms-calc((100% - 100px) / 2);
    padding: calc((100% - 100px) / 2);
    background-clip: content-box;
}

10 块级元素：inline-block

<div class="parent">
    <div class="child">child</div>
    <div class="brother">brother</div>
</div>

.parent {
    width: 400px;
    height: 400px;
    border: 1px solid red;
    position: relative;
}
.child, .brother {
    display: inline-block;
    vertical-align: middle;
}
.child {
    background: blue;
    font-size: 12px;
}
.brother {
    height: 400px;
    font-size: 0;
}

摘自：https://juejin.im/post/5a7a9a545188257a892998ef