A little history
Requiring images for decorative corners is a maintenance nightmare. The extra http requests to serve the images slowed down the page load and added to site bandwidth. Rounded corners require either 4 separate images — one for each corner — or a larger sprite image that includes all 4 corners if the design allows, which requires the addition of three, and sometimes 4, hooks for those corners.
And for what? A little decoration.
No more! Enough with markup clutter, extra http requests for decorative images
The CSS3 border-radius property is not supported on over 60% of the browsers surfing the web. So, why aren’t you using them? The CSS3 border-radius property allows you to create native rounded corners using only CSS. No divitis. No classitis. No extra http requests. No wasted hours in Photoshop.
The border radius property first raised it’s beautiful little head in 2005. Webkit was the first to support the border-radius property, but seemingly is the last to fully support it (more about that later).
With the border-radius property, you can create rounded corners without images in all modern browsers and IE9. You can create rounded corners, elliptical corners, uneven corners and odd effects.
So, how do you create these rounded corners? The syntax is slightly different for rounded corners than for elliptical corners. You can created 4 identical rounded corners with a single value, declare up to four different values — one for each rounded corner, or declare uneven corners by separating the horizontal radius from the vertical radius declarations with a slash in the shorthand or space in the long hand.
Most designs call for rounded corners, so let’s start with round corners first:
The syntax (round corners):
You can use the shorthand to declare identical (declare one value) or up to four different sized corner radii. Or, you can use the long hand to declare each corner separately:
border-radius: <TL & BR> <TR & BL>;
border-radius: <TL> <TR> <BR> <BL>;
Generally, you will want all four corners to have the same look and feel, so you will want all four corners to be equal EXCEPT in the case of top navigation bar tabs, where you will want the top corners to be round and the bottom corners to be rectangular.
You can use the shorthand:
border-radius: 0.5em 0.5em 0 0;
or you can use the longhand:
The above will create rounded corners: the vertical and horizontal sides of each corner will be the same: the horizontal radius is the same as the vertical radius. But what if you want elliptical corners? Rounded, but not actually round? Border radius allows for that.
The syntax (rounded or elliptical corners):
If you want rounded corners that are elliptical instead of round, there’s a syntax for that. In the shorthand syntax, separate the horizontal radius from the vertical radius declarations with a slash.
border-radius: <vertical-radius values> / <horizontal-radius values>;
border-radius: <TL & BR> <TR & BL> / <TL & BR> <TR & BL>;
border-radius: <TL> <TR> <BR> <BL> / <TL> <TR> <BR> <BL> ;
If you are using the longhand properties, separate the two radii with a space instead. Notice the values above have a slash, the values below do not.
border-top-right-radius: <TR vertical> <TR horizontal>;
border-bottom-right-radius: <BR vertical> <BR horizontal>;
border-bottom-left-radius: <BL vertical> <BL horizontal>;
border-top-left-radius: <TL vertical> <TL horizontal>;
These two declarations are equivalent
border-radius: 2em 1em 4em 3em/ 0.5em 3em;
border-top-left-radius: 2em 0.5em;
border-top-right-radius: 1em 3em;
border-bottom-right-radius: 4em 0.5em;
And now for the bad news
While border-radius property has widespread browser support, there are some discrepancies in browser support.
Older Internet Explorer versions
Border-radius is not supported in IE6, IE7 or IE8. Remember that users access your web site with only one browser. They don’t look at all the different browsers: only web developers do that. So, visitors using these browsers will not see your beautifully rounded corners, but they also won’t know that they are missing anything. Rounded corners are an enhancement. They’re generally not critical to the content of your site. There’s an HTC file called CSS Curved Corner by Remiz Rahnas that can create rounded corner effects for old versions of IE.
Older non-IE browsers that are still lingering
If you’re still supporting Firefox 3.6 and or Safari 4 you’ll want to add the -moz- and -webkit- vendor prefixes respectively. Since Safari 5 was released over a year ago, and Safari 4 has less than 0.75% market share, I have dropped the -webkit- prefix syntax. At the time of this writing, while Firefox 4 has surpassed Firefox 3.6 in the USA market, the trend is not worldwide, so I am still including -moz- prefixed corners. Also, older versions of Firefox used a non-standards syntax for the long hand, so when declaring -moz- prefixed border radii, use the shorthand. If you want to use the long hand, I recommend using the border radius generator to get the FF3.6 and Safari 4 and earlier long hand markup.
Quirks in Modern Browsers
Opera, IE9, Safari 5, Firefox 4 and Chrome all understand the vendorless recommended standard syntax for the four long hand properties and the single shorthand border-radius property, but some browsers do have some bugs:
Safari 5 does not understand percentage values for rounded corners. This is resolved in the webkit nightly builds, so will be resolved in Safari 6. In the meantime, since it doesn’t understand %, it will ignore the entire declaration. The hack is to declare the border radius in other length units first, then declare your percent version for all browsers that do understand percentage values.
Opera currently also have bugs with percentage values. It does understand percents, but does not render them correctly in some cases. The values in elliptical corners is slightly off, and has been fixed in the Opera Next build (build 1024), so will be fixed in their next launch most likely. In most cases, therefore, a hack may not be necessary. When an element is floated, the border radius is completely off in Opera. The border-radius is huge, making the element look almost rectangular, as if there were no border-radius set. If you’re ok with graceful degradation, the Opera user won’t be negatively impacted: they will just see almost what IE 7 users see. If you’re not OK with that, either don’t float your rounded elements if you’ve used percentage values as your radius length, or use other length types (em, px, etc) if your element is floated.