The border-radius property is supported in IE9+, Firefox 4+, Chrome, Safari 5+, and Opera, because it is CSS3 property. The syntax is:
border-radius: 1-4 length|% / 1-4 length|%;
Example 1
border-radius:2em;
is equivalent to:
border-top-left-radius:2em;
border-top-right-radius:2em;
border-bottom-right-radius:2em;
border-bottom-left-radius:2em;
Example 2
border-radius: 2em 1em 4em / 0.5em 3em;
is equivalent to:
border-top-left-radius: 2em 0.5em;
border-top-right-radius: 1em 3em;
border-bottom-right-radius: 4em 0.5em;
border-bottom-left-radius: 1em 3em;
See more detailed explanation and tips and tricks for border radius here.