CSS3 animations allow you to alter the values of CSS properties over time. They’re now supported in Firefox 5+, Chrome, Safari 4+, iOS, Android 4+, and the upcoming IE10, therefore, using them in real production websites is possible. One of the cool things you can do with them is change the color of an element using exclusively CSS. Previously a technique like this was only possible using JavaScript’s setInterval function to gradually change the appropriate property of the element. See jQuery UI’s animate demos for a good example.

Getting Started

Let’s start with a basic example (note - Whether or not you see the animation depends on whether your browser supports CSS3 animations. You can check at caniuse.com.

Syntax

Let’s break this down how this works one section at a time.

div {
	-webkit-animation: color_change 1s infinite alternate;
	-moz-animation: color_change 1s infinite alternate;
	-ms-animation: color_change 1s infinite alternate;
	-o-animation: color_change 1s infinite alternate;
	animation: color_change 1s infinite alternate;
}

The animation property is how you define a CSS3 animation. The MDN (Mozilla Developer Network) docs have extensive documentation on all the various sub properties available to configure the animation here. In this example I’m setting…

• color_change - This refers to a named @keyframes rule, which we’ll get into in a minute.
• animation_duration: 1s - The animation should last 1 second.
• animation_iteration_count: infinite - The animation will cycle forever.
• animation_direction: alternate - This will tell the animation to alternate, from start to end, then end to start, then start to end, and so on. In this example it keeps the box from being jerky by quickly switching from red to blue.

For readability you can also list the properties out individually.

/* Note: Prefixes omitted, see below */
div {
	animation-name: color_change;
	animation-duration: 1s;
	animation-iteration-count: infinite;
	animation-direction: alternate;
}

Prefixes

The vendor prefixes are necessary because CSS3 animations are still considered an experimental feature (the spec is still in working draft status. However, the syntax is consistent across modern browsers, so you only have to copy and paste the code to add all the necessary prefixes. Always include the un-prefixed property last to make your code future friendly to browsers that add un-prefixed support. For an up to date list of what browsers support CSS3 animations and which prefixes to use check out the CSS animation page at caniuse.com.

If you get sick of typing out all the vendor prefixes you’re not alone. -prefix-free is a tool by Lea Verou that lets you write your CSS unprefixed. A JavaScript file detects whether a browser prefix is necessary, which one to use, and applies it automatically.

Another option is Prefixr by Jeffrey Way of nettuts. It lets you copy and paste your code in, run it, and have the appropriate prefixes added automatically.

Browser prefixes have been been a hot topic lately after it was announced that IE, Firefox, and Opera are considering adopting support for -webkit prefixes. If you’re curious a number of others have written about this.

Keyframes

@-webkit-keyframes color_change {
	from { background-color: blue; }
	to { background-color: red; }
}
@-moz-keyframes color_change {
	from { background-color: blue; }
	to { background-color: red; }
}
@-ms-keyframes color_change {
	from { background-color: blue; }
	to { background-color: red; }
}
@-o-keyframes color_change {
	from { background-color: blue; }
	to { background-color: red; }
}
@keyframes color_change {
	from { background-color: blue; }
	to { background-color: red; }
}

Keyframes are a way of specifying a set of properties and their values at different states of an animation. @keyframes color_change gives the @keyframes a name of color_change. This provides the connection used on the animation property above.

from { background-color: blue; }
to { background-color: red; }

This animation only has 2 steps, a start and an end. Since such animations are quite common, the spec provides the keywords from and to for defining the state of properties at the beginning and end of the animation. This could also have been written using percentages for the steps.

0% { background-color: blue; }
100% { background-color: red; }

If the animation has more than 2 steps, they can be listed using multiple steps as such.

0% { background-color: blue; }
25% { background-color: orange; }
50% { background-color: yellow; }
75% { background-color: black; }
100% { background-color: red; }

Real-World Example

Since the first demo was rather contrived, I thought I’d provide an example of how you could use this technique in the real world. On buttons, a common UI pattern is to provide the user with visual feedback that they’re on the button by applying a subtle color change. This is usually done by applying a different background-color on the hover pseudoclass of the button as such:

button {
	background-color: pink;
}
button:hover {
	background-color: hotpink;
}

To improve upon this, we can add a CSS 3 color animation to gradually make the color transition. The following example shows each side by side:

Falling Back Gracefully

Since CSS3 animations are only present in modern browsers, there’s a good chance a number of your users won’t have them available. Luckily, CSS3 animations fallback gracefully to browsers that don’t support them. If the browser doesn’t know how to handle a CSS animation, it just ignores the CSS rules. Therefore, make sure not to use CSS animations to perform functionality that is vital to your site or application, it should simply enhance the user experience.

In the button example above if the browser can’t perform the animation, the animated button will simply fallback on the hover button’s behavior.

button {
	background-color: pink;
}
button:hover {
	/* IE <= 6 get no hover effect */
	/* All browsers IE 7+ know how to handle this */
	background-color: hotpink;
	
	/* Browsers that support CSS animations get the animation, */
	/* those that don't ignore this and move on. */
	/* Note: I've omitted the vendor prefixes for simplicity. */
	animation: color_change 1s;
}

Detect Support and Polyfill

If you have a CSS color animation that you absolutely must have work on all browsers back to IE6, you can do so by detecting support via Modernizr, and falling back to jQuery UI’s animation.

if (!Modernizr.cssanimation) {
	$('button').on('mouseover', function() {
		//jQuery UI doesn't support the hotpink keyword :(
		$(this).animate({ backgroundColor: '#FF69B4' }, 1000);
	}).on('mouseout', function() {
		$(this).stop(true, true);
		$(this).css('backgroundColor', 'pink');
	});
}

Live example (this should work across all browsers):

If the jQuery UI approach already works cross browser why would you bother doing this with CSS?

• Certain desktop and mobile browsers can use hardware acceleration with CSS3 animations. This usually results in the animation rendering smoother.
• Users with JavaScript disabled will still see the animation.
• If you’re only using jQuery & jQuery UI for this animation you can save yourself two HTTP requests by using Modernizr’s load function. This will first test whether the browser supports CSS animations, if it does nothing needs to be done, if it doesn’t all scripts listed in the nope parameter will be loaded.

Modernizr.load({
	test: Modernizr.cssanimation,
	nope: ['jquery.js', 'jquery-ui']
});

Summary

CSS 3 color animations can be used in modern browsers today. For most use cases no animations in unsupported browsers isn’t a problem, and, if it is, jQuery UI can be used to polyfill the functionality.