css居中方法

行内元素

1、水平居中

• text-align:center;

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

.parent{
    background-color:red;
    text-align:center;
}

• fit-content;

  .parent{
      background-color:red;
      width:fit-content;
  }

2、垂直居中

• line-height(单行文本）

.parent{
    height:200px;
    line-height:200px;
    background-color:red;
}

块级元素

1、水平居中

• margin:0 auto;

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

.parent{
    background-color:red;
}
.child{
    width:100px;
    margin:0 auto;
    background-color:blue;
}

2、水平垂直居中

• 定位

.parent{
    position:relative;
    height:200px;
    background-color:red;
}
.child{
    weight:100px;
    height:100px;
    position:absolute;
    background:blue;
    left:calc(50%-50px);
    top:calc(50%-50px);    
}

.parent{
    position:relative;
    height:200px;
    background-color:red;
}
.child{
    weight:100px;
    height:100px;
    position:absolute;
    background:blue;
    left:50%;
    top:50%;
    margin-top:-50px;
    margin-left:-50px;
}

• 定位+transform

.parent{
    position:relative;
    height:200px;
    background-color:red;
}
.child{
    position:absolute;
    background:blue;
    left:50%;
    top:50%;
    transform:translate(-50%,-50%);
}

• 定位+margin

.parent{
    position:relative;
    height:200px;
    background-color:red;
}
.child{
    width:100px;
    height:100px;
    position:absolute;
    left:0;
    right:0;
    top:0;
    botttom:0;
    margin:auto;
    background:blue;
}

• padding

.parent{
    padding:20px;
    background-color:red;
}
.child{
    height:200px;
    background:blue;
}

• flex

.parent{
    height:200px;
    display:flex;
    align-items:center;     //垂直居中
    justify-content:center; //水平居中
    background-color:red;
}
.child{
    width:100px;
    height:100px;
    background-color:blue;
}

• 伪元素

.parent{
    height:200px;
    text-align:center;
    background-color:red;
}
.child{
    width:100px;
    height:100px;
    display:inline-block;
    vertical-align:middle;
    background-color:blue;
}
.parent::before{
    content:"";
    width:20px;
    height:200px;
    display:inline-block;
    vertical-align:middle;
    background-color:yellow;
}

• calc（宽高相等）

  .parent{
      width:600px;
      height:600px;
      background-color:red;
  }
  .child{
      width:100px;
      height:100px;
      padding:calc((100%-100px)/2);
      background-clip:content-box;
      background-color:blue;
  }