内部元素横向&&垂直居中的15种常见写法

摘要：非常简洁易懂，排名不分先后，开整第一种常见的第二种第三种通过的第四种标配标配标配三个标配一起使用才能发挥作用第五种，不能大量使用，会影响性能第六种第七种第八种第九种第十种第十一

非常简洁易懂，排名不分先后，开整！
HTML:

.main {
            position: relative;
            width: 800px;
            height: 500px;
            background-color: lightblue;
        }
        
        .content {
            position: absolute;
            width: 300px;
            height: 200px;
            top: 50%;
            left: 50%;
            margin-left: -150px;
            margin-top: -100px;
            background: lightpink;
        }

.main {
            position: relative;
            width: 800px;
            height: 500px;
            background-color: lightblue;
        }
        
        .content {
            position: absolute;
            width: 300px;
            height: 200px;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
            background: lightpink;
        }

.main {
            position: relative;
            width: 800px;
            height: 500px;
            background-color: lightblue;
        }
        
        .content {
            position: absolute;
            width: 300px;
            height: 200px;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            background: lightpink;
            margin: auto;
        }

.main {
            width: 800px;
            height: 500px;
            background: lightblue;
            display: table-cell;
            /*标配*/
            vertical-align: middle;
            /*标配*/
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
            margin: auto;
            /*标配*/
        }
        /*三个标配一起使用才能发挥作用*/

 .main {
            width: 800px;
            height: 500px;
            background-color: lightblue;
        }
        
        .content {
            width: 300px;
            height: 70px;
            background: lightpink;
            margin: auto;
            position: relative;
            top: calc((100% - 70px)/2);
        }

 .main {
            display: flex;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            justify-content: center;
            align-items: center;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
        }

.main {
            display: flex;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            justify-content: center;
            text-align: center;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
            align-self: center;
        }

.main {
            display: flex;
            width: 800px;
            height: 500px;
            background-color: lightblue;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
            margin: auto;
        }

.main {
            display: grid;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            justify-content: center;
            align-content: center;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
        }

.main {
            display: grid;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            justify-content: center;
            align-items: center;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
        }

.main {
            display: grid;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            justify-content: center;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
            align-self: center;
        }

.main {
            width: 800px;
            height: 500px;
            display: grid;
            background: lightblue;
        }
        
        .content {
            width: 300px;
            height: 200px;
            margin: auto;
            background: lightpink;
        }

  .main {
            width: 800px;
            height: 500px;
            display: grid;
            place-content: center;
            /*这是justy-content与align-items的结合写法*/
            background-color: lightblue;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
        }

 .main {
            display: grid;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            place-items: center;
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
        }

.main {
            margin: auto;
            width: 800px;
            height: 500px;
            background-color: lightblue;
            display: grid;
            grid-template-columns: 1fr auto 1fr;
            grid-template-rows: 1fr auto 1fr;
            grid-template-areas: ". . ." ". amos ." ". . .";
        }
        
        .content {
            width: 300px;
            height: 200px;
            background: lightpink;
            grid-area: amos;
        }

好啦，十五种方法Get！