Code Snippet

Nested & Expandable Folders

Demo by Martin Ivanov utilizing hidden checkboxes and adjacent sibling combinators to set the "state" of each folder.

.css-treeview ul,
.css-treeview li
{
	padding: 0;
	margin: 0;
	list-style: none;
}

.css-treeview input
{
	position: absolute;
	opacity: 0;
}

.css-treeview
{
	font: normal 11px "Segoe UI", Arial, Sans-serif;
	-moz-user-select: none;
	-webkit-user-select: none;
	user-select: none;
}

.css-treeview a
{
	color: #00f;
	text-decoration: none;
}

.css-treeview a:hover
{
	text-decoration: underline;
}

.css-treeview input + label + ul
{
	margin: 0 0 0 22px;
}

.css-treeview input + label + ul
{
	display: none;
}

.css-treeview label,
.css-treeview label::before
{
	cursor: pointer;
}

.css-treeview input:disabled + label
{
	cursor: default;
	opacity: .6;
}

.css-treeview input:checked:not(:disabled) + label + ul
{
	display: block;
}

.css-treeview label,
.css-treeview label::before
{
	background: url("icons.png") no-repeat;
}

.css-treeview label,
.css-treeview a,
.css-treeview label::before
{
	display: inline-block;
	height: 16px;
	line-height: 16px;,
	vertical-align: middle;
}

.css-treeview label
{
	background-position: 18px 0;
}

.css-treeview label::before
{
	content: "";
	width: 16px;
	margin: 0 22px 0 0;
	vertical-align: middle;
	background-position: 0 -32px;
}

.css-treeview input:checked + label::before
{
	background-position: 0 -16px;
}

/* webkit adjacent element selector bugfix */
@media screen and (-webkit-min-device-pixel-ratio:0)
{
	.css-treeview
	{
		-webkit-animation: webkit-adjacent-element-selector-bugfix infinite 1s;
	}

	@-webkit-keyframes webkit-adjacent-element-selector-bugfix
	{
		from
		{
			padding: 0;
		}
		to
		{
			padding: 0;
		}
	}
}

<div class="css-treeview">
	<ul>
		<li><input type="checkbox" id="item-0" /><label for="item-0">This Folder is Closed By Default</label>
			<ul>
				<li><input type="checkbox" id="item-0-0" /><label for="item-0-0">Ooops! A Nested Folder</label>
					<ul>
						<li><input type="checkbox" id="item-0-0-0" /><label for="item-0-0-0">Look Ma - No Hands!</label>
							<ul>
								<li><a href="./">First Nested Item</a></li>
								<li><a href="./">Second Nested Item</a></li>
								<li><a href="./">Third Nested Item</a></li>
								<li><a href="./">Fourth Nested Item</a></li>
							</ul>
						</li>
						<li><a href="./">Item 1</a></li>
						<li><a href="./">Item 2</a></li>
						<li><a href="./">Item 3</a></li>
					</ul>
				</li>
				<li><input type="checkbox" id="item-0-1" /><label for="item-0-1">Yet Another One</label>
					<ul>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
					</ul>
				</li>
				<li><input type="checkbox" id="item-0-2" disabled="disabled" /><label for="item-0-2">Disabled Nested Items</label>
					<ul>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
					</ul>
				</li>
				<li><a href="./">item</a></li>
				<li><a href="./">item</a></li>
				<li><a href="./">item</a></li>
				<li><a href="./">item</a></li>
			</ul>
		</li>
		<li><input type="checkbox" id="item-1" checked="checked" /><label for="item-1">This One is Open by Default...</label>
			<ul>
				<li><input type="checkbox" id="item-1-0" /><label for="item-1-0">And Contains More Nested Items...</label>
					<ul>
						<li><a href="./">Look Ma - No Hands</a></li>
						<li><a href="./">Another Item</a></li>
						<li><a href="./">And Yet Another</a></li>
					</ul>
				</li>
				<li><a href="./">Lorem</a></li>
				<li><a href="./">Ipsum</a></li>
				<li><a href="./">Dolor</a></li>
				<li><a href="./">Sit Amet</a></li>
			</ul>
		</li>
		<li><input type="checkbox" id="item-2" /><label for="item-2">Can You Believe...</label>
			<ul>
				<li><input type="checkbox" id="item-2-0" /><label for="item-2-0">That This Treeview...</label>
					<ul>
						<li><input type="checkbox" id="item-2-2-0" /><label for="item-2-2-0">Does Not Use Any JavaScript...</label>
							<ul>
								<li><a href="./">But Relies Only</a></li>
								<li><a href="./">On the Power</a></li>
								<li><a href="./">Of CSS3</a></li>
							</ul>
						</li>
						<li><a href="./">Item 1</a></li>
						<li><a href="./">Item 2</a></li>
						<li><a href="./">Item 3</a></li>
					</ul>
				</li>
				<li><input type="checkbox" id="item-2-1" /><label for="item-2-1">This is a Folder With...</label>
					<ul>
						<li><a href="./">Some Nested Items...</a></li>
						<li><a href="./">Some Nested Items...</a></li>
						<li><a href="./">Some Nested Items...</a></li>
						<li><a href="./">Some Nested Items...</a></li>
						<li><a href="./">Some Nested Items...</a></li>
					</ul>
				</li>
				<li><input type="checkbox" id="item-2-2" disabled="disabled" /><label for="item-2-2">Disabled Nested Items</label>
					<ul>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
						<li><a href="./">item</a></li>
					</ul>
				</li>
			</ul>
		</li>
	</ul>
</div>