Same border on all corners.
border-radius: 20px;
Different border on each corner.
border-radius: tl tr br bl;
Different border on each corner, set individually.
border-top-left-radius: 5px; etc.
Same elliptical border on all corners.
border-radius: x / y;
Different elliptical border on each corner.
border-radius: ulx urx lrx llx / uly ury lry lly;