头像、图片等作为背景出现，可以避免图片拉伸变形background-size: cover; background-position: 50%;

 

background-size: cover;
background-position: 50%;

 background:url("//mcake.oss-cn-hangzhou.aliyuncs.com/file/96514a3e5aa8f573/6cb309ee9fc7c4b1.jpg") no-repeat;