Creating an accordion using CSS transitions

An accordion effect can be achieved using CSS3’s :target pseudo-class, without requiring JavaScript. Using the proprietary -webkit-transition property this accordion can also be animated.

Result

CSS3 Accordion
Works in browsers that support the :target pseudo-class, see the Quirks Mode compatibility tables. Animation works in recent WebKit based browsers.

Experiment updated. Transitions are now widely supported, including Opera, Firefox and IE10.

How To

Each part of the accordion has an ID, heading and content region. The header includes a link that matches the section’s ID, whilst the content is wrapped in a container which will control its display.

<div class="accordion">
	<h2>Accordion Demo</h2>
	<div id="one" class="section">
		<h3>
			<a href="#one">Heading 1</a>
		</h3>
		<div>
			<p>Content</p>
		</div>
	</div>
	<div id="two" class="section">
		<h3>
			<a href="#two">Heading 2</a>
		</h3>
		<div>
			<p>Content</p>
		</div>
	</div>
</div>

The CSS then relies on the :target pseudo-class to apply different styles to the chosen section — increasing the height and, in large content cases, altering the overflow behaviour to allow scrolling. To animate the opening and closing of sections the -webkit-transition property is needed (documentation), in this case acting on the height attribute for a duration of 0.3 seconds using the ease-in timing function.

Stripping out the styling, the CSS boils down to:

.accordion h3 + div {
	height: 0;
	overflow: hidden;
	-webkit-transition: height 0.3s ease-in;
	-moz-transition: height 0.3s ease-in;
	-o-transition: height 0.3s ease-in;
	-ms-transition: height 0.3s ease-in;
	transition: height 0.3s ease-in;
}

.accordion :target h3 + div {
	height: 100px;
}

.accordion .section.large:target h3 + div {
	overflow: auto;
}

Critique

Obviously this approach has its limitations. Multiple open accordions on one page wouldn’t be possible — restricted by a URI’s one fragment identifier limit; as one accordion opens the other would lose the target and automatically close. Similarly, pages that use a fragment identifier for everyday use will notice oddities — take for instance when using top links to return to the top of the page, any accordion would, in this case, reset. Other uses include accessibility links and simulated page histories when using Ajax.

Paul Hayes

Paul Hayes is a developer at Last.fm. You should follow him on Twitter, where he talks about UX, HTML, CSS and JavaScript, amongst other cool stuff.