/* Mozilla */

-moz-border-radius:4px;
-moz-border-radius-topleft:4px;
-moz-border-radius-topright:4px;
-moz-border-radius-bottomleft:4px;
-moz-border-radius-bottomright:4px;

/* WebKit */

-webkit-border-radius:4px;
-webkit-border-top-left-radius:4px;
-webkit-border-top-right-radius:4px;
-webkit-border-bottom-left-radius:4px;
-webkit-border-bottom-right-radius:4px;

/* Standard */

border-radius:4px;
border-top-left-radius:4px;
border-top-right-radius:4px;
border-bottom-left-radius:4px;
border-bottom-right-radius:4px;

http://www.w3.org/TR/2005/WD-css3-background-20050216/#the-border-radius

Vendor prefixes and W3C standard for border-radius in CSS3.

CSS Rounded Corners with CSS3 Border Radius

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CSS