Oblong rectangle radius size is 1/2 of height where heigth > width Eclipse border-radius: 50% / 50%; where height > width
circle radius is 50% height, where h=w top only use border-radius-top or use four values first is top left then CW border-radius: 20px 20px 0px 0px;
exagerrated top radius; others set to a small redius
border-radius : 30px 30px 10px 10px;
set all radius to 10pixels; then set only top left radius larger
border-radius : 10px; border-top-left-radius: 60px;
first 4 values are the x width or length of radius; second four values after / are the Y radius height;
border-radius: 30px 0px 30px 0px / 90px 0px 90px 0px;

Same as previous example, but using specific property names
border-bottom-right-radius: 30px 90px;
border-top-left-radius: 30px 90px;

   

* Created using border radius - gave tight code but pixels only;

Another choice css3generator.com but too much output

Didn't find any full feature border-radius, you can set border images and x - width, and y - height radius separate.