1,父元素display: flex,子元素margin: auto;
2,父元素text-aligin: center,子元素display: inline-block;
3,父元素display: table-cell或者table,子元素 margin:auto;
4,子元素margin-left: auto;margin-right: auto;
5,子元素margin:0 auto;
6,子元素position: absolute;left: 50%;margin-left: -width/2;
7,子元素position: absolute;margin: auto;top: 0;left: 0;bottom: 0;right: 0;
8,子元素position: absolute;top: 50%;left: 50%;-webkit-transform:translate(-50%,-50%);  
9,没测试width:-webkit-fit-content;