CSS3 水平居中和垂直居中方式整合


實現居中的方式分為水平和垂直,接下來對兩種方式進行整體的整合

水平居中

水平居中需要滿足兩個條件:父級元素為塊級元素且設置寬度

1.子元素為任意元素,但未設置寬度

<body>
    <div class="wrap">
          <p class="center">快把我變居中<p/>
    </div>            
</body>

.wrap{
     width:300px;
     height:300px;      
background:gray; } .center{ text-align:center; }

效果如下圖:

 

2.子元素為任意元素,並設定了寬度

 

  • margin
<body>
    <div class="wrap">
          <p class="center">margin<p/>
    </div>            
</body>
.wrap{
     width:300px;
     height:300px;
background:gray; } .center{ margin:0 auto;
   width:100px;
}

效果圖如下:

 

  • padding-left和padding-right

我們還可以通過計算父元素和子元素寬度之差,(父寬-子寬)/2,得出父元素的padding-left或者padding-right

<div class="wrap">
    <div class="center">快把我變居中</div>
</div>
</body>
.wrap{
    width:300px;
    height:300px;
    background: gray;
    box-sizing: border-box;
    padding-left: 100px;
}

.center{
    color: beige;
    box-sizing: border-box;
    width: 100px;
}

效果如圖:

 

  • 計算子元素的margin-left或margin-right

計算子元素的方式和計算父元素的方式相同

<div class="wrap">
    <div class="center">margin-left</div>
</div>
.wrap{
    width:300px;
    height:300px;
    background: gray;
    box-sizing: border-box;
}

.center{
    color: beige;
    box-sizing: border-box;
    width: 100px;
    margin-left: 100px;
}

效果如圖:

 

  • 使用定位
<div class="wrap">
    <div class="center">margin-left</div>
</div>
.wrap{
    width:300px;
    height:300px;
    background: gray;
    box-sizing: border-box;
    position: relative;
}

.center{
    color: beige;
    box-sizing: border-box;
    position: absolute;
    left: 50%;
    margin-left: -50px;
    width: 100px;
}

效果如圖:

  • flex
<body>
<div class="wrap">
    <div class="center">flex</div>
</div>
</body>
.wrap{
    width:200px ;
    height: 300px;
    border: 2px solid #ccc;
    box-sizing: border-box;
    display: flex;
    justify-content: center;
    flex-direction: row;
}

.center{
    width:100px ;
    height: 100px;
    box-sizing: border-box;
    background: #6495ed;
    color: #fff;

}

 

垂直居中

 

1.子元素為塊級元素,寬高設定了

  • 計算父元素的padding-top或padding-bottom
<body>
<div class="wrap">
    <div class="center">margin-top</div>
</div>
</body>
.wrap{
    width:200px ;
    height: 300px;
    border: 2px solid #ccc;
    box-sizing: border-box;
    padding-top: 100px;
}

.center{
    width:100px ;
    height: 100px;
    box-sizing: border-box;
    background: #6495ed;
    color: #fff;
}

效果如圖:

  • 計算子元素的margin-top或margin-bottom
<body>
<div class="wrap">
    <div class="center">position</div>
</div>
</body>
.wrap{
    width:200px ;
    height: 300px;
    border: 2px solid #ccc;
    box-sizing: border-box;
}

.center{
    width:100px ;
    height: 100px;
    box-sizing: border-box;
    background: #6495ed;
    margin-top: 100px;
    color: #fff;
}

 

  • 定位
<body>
<div class="wrap">
    <div class="center">padding-top</div>
</div>
</body>
.wrap{
    width:200px ;
    height: 300px;
    border: 2px solid #ccc;
    box-sizing: border-box;
    position: relative;
}

.center{
    position: absolute;
    width:100px ;
    height: 100px;
    box-sizing: border-box;
    background: #6495ed;
    color: #fff;
    top: 50%;
    margin-top: -50px;
}

效果如圖:

  • flex
<body>
<div class="wrap">
    <div class="center">position</div>
</div>
</body>
.wrap{
    width:200px ;
    height: 300px;
    border: 2px solid #ccc;
    box-sizing: border-box;
    display: flex;
    justify-content: center;
    flex-direction: column;
}

.center{
    width:100px ;
    height: 100px;
    box-sizing: border-box;
    background: #6495ed;
    color: #fff;

}

效果如圖:

 


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