display 垂直居中

/* Center slide text vertically */
display: -webkit-box;
display: -ms-flexbox;
display: -webkit-flex;
display: flex;  
-webkit-box-pack: center;
-ms-flex-pack: center;
-webkit-justify-content: center;
justify-content: center;
-webkit-box-align: center;
-ms-flex-align: center;
-webkit-align-items: center;
align-items: center;