css3画圆/椭圆

border-radius取长宽的一半

div
{
height: 100px;
width: 100px;
border-radius: 50px;
background: blue;
}

椭圆

只要长宽不相等

div
{
height: 100px;
width: 100px;
border-radius: 50px;
padding:10px 50px;
background: blue;
}