<!-- <div class="radius-test1"></div>
-->
<div class="semi-circle"></div>
.radius-test1 {
width: 300px;
height: 200px;
background-color: #f00;
border: 50px solid #cd0000;
border-radius: 300px/200px;
}
.semi-circle
{
width:100px;
height:50px;//高度是宽度的一半
background-color:#f00;
border-radius:50px 50px 0 0;//左上和右上至少为height值
}