关于元素居中之我见（干货）

1   .first{
2     width: 300px;
3     height: 100px;
4     background-color: black;
5     color: white;
6     text-align: center;
7     margin: 0 auto; //针对块级元素
8 
9   }

1   <div class="first">
2     不使用定位（1）
3   </div>

  .second{
    width: 300px;
    height: 100px;
    background-color: green;
  }
  .s_child{
    width: 150px;
    line-height: 100px;
  }

  <div class="second">
    <div class="s_child">
      不使用定位（2）
    </div>
  </div>

.dw_one{
      width: 600px;
      height: 300px;
      position: absolute;
      background: black;

    }
    .dw_one_child{
      background: white;
      position: relative;
      width: 50px;
      height: 50px;
      top: 50%;
      left: 50%;
      margin-top: -25px;
      margin-left: -25px;
    }

  <div class="dw_one">
    <div class="dw_one_child">
      a
    </div>
  </div>

  .wrapper{
      width: 600px;
      height: 600px;
    }
    .dw_two{
      width: 100%;
      height: 100%;
      position: absolute;
      background: black;

    }
    .dw_two_child{
      background: white;
      position: relative;
      top: 50%;
      left: 50%;
      width: 100px;
      height: 100px;
      transform:translate(-50%, -50%);
      -moz-transform:translate(-50%, -50%);
      -ms-transform:translate(-50%, -50%);
      -o-transform:translate(-50%, -50%);
      -webkit-transform:translate(-50%, -50%);
    }

1 <div class="wrapper">
2   <div class="dw_two">
3       <div class="dw_two_child">
4         a
5       </div>
6   </div>
7 </div>

 1   #outer{
 2            width: 200px;
 3            height: 200px;
 4            background: #cccccc;
 5            display: table;
 6            _position: relative;   // "_"为了兼容IE6
 7        }
 8        #inner{
 9            display: table-cell;
10            vertical-align: middle;
11            _position: absolute;
12            _top: 50%;
13        }
14        #content{
15            _position: relative;
16            _top: -50%;
17        }

1 <div id="outer">
2     <div id="inner">
3         <div id="content">
4           Paradise_追逐者所写的居中问题总结之我见
5         </div>
6     </div>
7 </div>