弹性盒模型（上下左右居中）(移动端)兼容性

display: -webkit-box;
display: -moz-box;
display: -ms-flexbox;
display: -o-box;
display: box;
display: -webkit-flex; /* Safari */
display: flex;
justify-content: center;
-webkit-box-align: center;
-webkit-align-items: center;
-ms-flex-align: center;
align-items: center;