1 div{
 2     width:200px;
 3     height:100px;
 4     border-radius:50%
 5 }
 6 
 7 等价于
 8 
 9 div{
10     width:200px;
11     height:100px;
12     border-radius:100px/50px;
13 }
14 
15 就变成了椭圆说明代码