水平居中：
内联元素：text-align:center;相对于父级居中显示
块级元素：margin:0 auto;但是需要同时width，否则无法看到效果
多个块级元素居中：在此想要探讨一下display:inline-block;和display:flex;
方法1：在父级上设置text-align:center;在元素上设置:display:inline-block;同时为了使文字向左显示，设置了text-align:left;在浏览器中的显示为，子元素高度自适应，底部对齐。
方法2：在子元素上设置display:center;justify-content:center;子元素的高度一致，与元素中内容最多的高度相同。
二种方法在谷歌，火狐，360均兼容，但是第2种方法在IE10中不兼容，之前的IE版本可想也是不兼容的。当然在此也要处理由于浮动导致离层，父级背景颜色加不上去的问题。
1 <main class="inline-block-center"> 2 <div> 3 I'm an element that is block-like with my siblings and we're centered in a row. 4 </div> 5 <div> 6 I'm an element that is block-like with my siblings and we're centered in a row. I have more content in me than my siblings do. 7 </div> 8 <div> 9 I'm an element that is block-like with my siblings and we're centered in a row.10 </div>11 </main>
1 <main class="flex-center"> 2 <div> 3 I'm an element that is block-like with my siblings and we're centered in a row. 4 </div> 5 <div> 6 I'm an element that is block-like with my siblings and we're centered in a row. I have more content in me than my siblings do. 7 </div> 8 <div> 9 I'm an element that is block-like with my siblings and we're centered in a row.10 </div>11 </main>
1 body { 2 background: #f06d06; 3 font-size: 80%; 4 } 5 main { 6 background: white; 7 margin: 20px 0; 8 padding: 10px; 9 }10 main div {11 background: black;12 color: white;13 padding: 15px;14 max-width: 125px;15 margin: 5px;16 }17 .inline-block-center {18 text-align: center;19 }20 .inline-block-center div {21 display: inline-block;22 text-align: left;23 }24 .flex-center {25 display: flex;26 justify-content: center;27 }垂直居中：
方法1：设置padding-top和padding-bottom的值相等
方法2：设置height和line-height的值相等
方法3：固定高度可以有一种处理方式position:absolute;top:50%;height:100px;margin-top:-50px;如果高度不固定，也可以使用js动态获取高度来。
还有css3的一些属性，考虑到兼容性问题不在叙述。
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