• CSS3 水平居中和垂直居中方式整合


    实现居中的方式分为水平和垂直,接下来对两种方式进行整体的整合

    水平居中

    水平居中需要满足两个条件:父级元素为块级元素且设置宽度

    1.子元素为任意元素,但未设置宽度

    <body>
        <div class="wrap">
              <p class="center">快把我变居中<p/>
        </div>            
    </body>

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

    效果如下图:

     

    2.子元素为任意元素,并设定了宽度

     

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

    效果图如下:

    • padding-left和padding-right

    我们还可以通过计算父元素和子元素宽度之差,(父宽-子宽)/2,得出父元素的padding-left或者padding-right

    <div class="wrap">
        <div class="center">快把我变居中</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;
    }

    效果如图:

    • 计算子元素的margin-left或margin-right

    计算子元素的方式和计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;
    }

    效果如图:

    • 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;
    }

    效果如图:

    • 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.子元素为块级元素,宽高设定了

    • 计算父元素的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;
    }

    效果如图:

    • 计算子元素的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;
    }

    效果如图:

    • 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;
    
    }

    效果如图:

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  • 原文地址:https://www.cnblogs.com/xx929/p/10156927.html
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