one-value syntax: the single value defines the radius
of all corners.
two-value syntax: the first value defines the radius
of top-left and bottom-right corner, while the second value defines
the radius of top-right and bottom-left sides corner.
three-value syntax: the first value defines the
radius of top-left corner, the second value defines the radius of
top-right and bottom-left corner, and the third value defines the
radius of bottom-right corner.
four-value syntax: each value defines the radius of
the border individually in the order top-left, top-right,
bottom-right, and bottom-left corner.
Warning: Internet Explorer 8 and earlier versions
don't support the
border-radius
property.