Rounded Corners with CSS3 Border Radius
The CSS3 Module has border-radius property using which you can achieve rounded corners without using images or other ugly hacks. This CSS property/feature is already widely known and used.
Official Spec URL: http://www.w3.org/TR/css3-background/#the-border-radius.
If you would like to technically understand how this works, then read the spec above that has some good diagrams explaining it. One of them is this:
This diagram is for border-radius: 55pt/25pt. Whenever using border-radius you can imagine 4 circles or ellipse at each corner whose radius is the specified px, pt, em, % or any other unit away from the box's sides (or basically the circle/ellipse itself).
Note: No support in Internet Explorer 8 and below.
Related:
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