有没有办法剪切 div 背景以暴露下面的图层？，就像这样：
to this:
欢迎任何前沿的 CSS 规则！
UPDATE
好的，我做了一个示例代码：http://jsfiddle.net/coma/9ae7g/1/ http://jsfiddle.net/coma/9ae7g/1/
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>Menu</title>
<style type="text/css">
@charset 'UTF-8';
body {
padding: 0;
margin: 0;
font-family: "Lucida Grande", "Lucida Sans Unicode", Tahoma, Verdana, Arial, sans-serif;
font-size: 12px;
background: #fff url("http://colourlovers.com.s3.amazonaws.com/images/patterns/1762/1762793.png?1314797062");
}
a {
text-decoration: none;
}
#menu {
position: fixed;
top: 0;
left: 0;
bottom: 0;
width: 250px;
}
body.wide>#menu {
width: 0;
}
#menu * {
line-height: 1em;
}
#menu:after {
content: '';
position: absolute;
top: 0;
right: 0;
width: 5px;
height: 100%;
border-right: 1px solid #666;
pointer-events: none;
background: -moz-linear-gradient(left, rgba(0,0,0,0) 0%, rgba(0,0,0,0.25) 100%);
background: -webkit-linear-gradient(left, rgba(0,0,0,0) 0%,rgba(0,0,0,0.25) 100%);
background: -o-linear-gradient(left, rgba(0,0,0,0) 0%,rgba(0,0,0,0.25) 100%);
background: -ms-linear-gradient(left, rgba(0,0,0,0) 0%,rgba(0,0,0,0.25) 100%);
background: linear-gradient(to right, rgba(0,0,0,0) 0%,rgba(0,0,0,0.25) 100%);
}
#menu ul, #menu li {
padding: 0;
margin: 0;
list-style: none;
background-color: #fafafb;
}
#menu li {
position: relative;
}
#menu>a {
position: absolute;
left: 100%;
top: 50%;
z-index: 1;
display: block;
width: 10px;
height: 20px;
margin: -10px 0 0 0;
text-indent: -100em;
overflow: hidden;
border-radius: 0 2px 2px 0;
background-color: #666;
transition: background-color .3s ease-out;
-moz-transition: background-color .3s ease-out;
-webkit-transition: background-color .3s ease-out;
-o-transition: background-color .3s ease-out;
-ms-transition: background-color .3s ease-out;
}
#menu>a:before {
position: absolute;
top: 5px;
right: 4px;
display: block;
content: '';
border-width: 5px 6px 5px 0;
border-style: solid;
border-color: transparent #fff transparent transparent;
}
body.wide>#menu>a:before {
right: 2px;
border-width: 5px 0 5px 6px;
border-color: transparent transparent transparent #fff;
}
#menu>ul {
height: 100%;
background-color: #888;
overflow: hidden;
}
#menu>ul span, #menu>ul a {
display: block;
padding: .4em;
color: #666;
font-weight: bold;
border-bottom: 1px solid #999;
}
#menu>ul a {
border-top: 1px solid #fff;
border-bottom: 1px solid #e9ecee;
}
#menu>ul>li>span {
font-size: 1.25em;
font-weight: bold;
color: #666;
text-shadow: 0 1px 1px #fff;
background-color: #eee;
background-image: -moz-linear-gradient(top, rgba(0,0,0,0) 0%, rgba(0,0,0,0.2) 100%);
background-image: -webkit-linear-gradient(top, rgba(0,0,0,0) 0%, rgba(0,0,0,0.2) 100%);
background-image: -o-linear-gradient(top, rgba(0,0,0,0) 0%, rgba(0,0,0,0.2) 100%);
background-image: -ms-linear-gradient(top, rgba(0,0,0,0) 0%, rgba(0,0,0,0.2) 100%);
background-image: linear-gradient(top, rgba(0,0,0,0) 0%, rgba(0,0,0,0.2) 100%);
cursor: pointer;
transition: background-color .4s;
-moz-transition: background-color .4s;
-webkit-transition: background-color .4s;
-o-transition: background-color .4s;
-ms-transition: background-color .4s;
}
#menu>ul>li>span:hover {
background-color: #fff;
}
#menu>ul>li>ul {
display: none;
}
#menu>ul>li.opened>ul, #menu>ul>li.current_ancestor>ul {
display: block;
}
#menu>ul>li>ul>li>a {
font-size: 1.2em;
color: #4183c4;
transition: background-color .4s;
-moz-transition: background-color .4s;
-webkit-transition: background-color .4s;
-o-transition: background-color .4s;
-ms-transition: background-color .4s;
}
#menu>ul>li>ul>li.current>a, #menu>ul>li>ul>li.current>a:hover {
color: #fff;
background-color: #39f;
border-color: #39f;
}
#menu>ul>li>ul>li.current:after {
content: '';
position: absolute;
right: -1px;
top: 50%;
margin: -9px 0 0 0;
display: block;
border-width: 10px 10px 10px 0;
border-style: solid;
border-color: transparent #fff transparent transparent;
z-index: 1;
}
#menu>ul>li>ul>li>a:hover {
background: #fff;
}
#menu>ul>li>ul>li:last-child {
border-bottom: 1px solid #aaa;
}
#menu>ul>li>ul>li[data-count]:after {
position: absolute;
top: 50%;
right: 14px;
display: block;
content: attr(data-count);
padding: .26em .5em;
background-color: #fff;
border-radius: 8px;
font-size: 12px;
margin: -9px 0 0 0;
color: #777;
border-top: 1px solid #ccc;
}
#section {
height: 2000px;
}
</style>
</head>
<body>
<div id="menu">
<a title="cerrar o abrir el menú" href="#">toggle</a>
<ul>
<li class="first opened">
<span>Usuario</span>
<ul class="menu_level_1">
<li class="first">
<a href="/logout">Logout</a>
</li>
<li class="current">
<a href="/">Home</a>
</li>
<li>
<a href="/user/">Usuarios</a>
</li>
<li class="last">
<a href="/discount/">Descuentos</a>
</li>
</ul>
</li>
<li>
<span>Artistas</span>
<ul class="menu_level_1">
<li class="first">
<a href="/artist/">Artistas</a>
</li>
<li class="last">
<a href="/artists/top10">Top 10 (3)</a>
</li>
</ul>
</li>
<li>
<span>Obras</span>
<ul class="menu_level_1">
<li class="first">
<a href="/artwork/">Obras</a>
</li>
<li>
<a href="/artworks/destacadas">Destacadas (4)</a>
</li>
<li class="last">
<a href="/artworks/ofertas">Ofertas (3)</a>
</li>
</ul>
</li>
<li>
<span>Pedidos</span>
<ul class="menu_level_1">
<li class="first last">
<a href="/order/">Pedidos</a>
</li>
</ul>
</li>
<li>
<span>Blog</span>
<ul class="menu_level_1">
<li class="first">
<a href="/article/">Artículos</a>
</li>
<li class="last">
<a href="/category/">Categorías</a>
</li>
</ul>
</li>
<li class="last">
<span>Newsletter</span>
<ul class="menu_level_1">
<li class="first last">
<a href="/newsletter/">Emails</a>
</li>
</ul>
</li>
</ul>
</div>
<div id="section"></div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function() {
var style = {
opened: 'opened',
wide: 'wide',
currentAncestor: 'current_ancestor'
};
var menu = $('#menu');
var items = $('#menu>ul>li');
var body = $('body');
items.filter('.' + style.currentAncestor)
.removeClass(style.currentAncestor)
.first()
.addClass(style.opened);
items.children('span').click(function(event) {
event.preventDefault();
var group = $(this).parent();
if(!group.hasClass(style.opened)) {
items.filter('.' + style.opened).removeClass(style.opened);
group.addClass(style.opened);
}
});
menu.children('a').click(function(event) {
event.preventDefault();
body.toggleClass(style.wide);
});
});
</script>
</body>
</html>
小鸟背景和高度为2000px的#section只是为了通过移动内容进行测试。
谢谢大家！
