<style type="text/css">
/*Fontawesome Iconfont*/
@import url(http://libs.useso.com/js/font-awesome/4.0.1/css/font-awesome.min.css)
@import url(http://fonts.useso.com/css?family=Montserrat)
* {margin: 0padding: 0}
li {list-style-type: none}
.grid {float: leftwidth:980pxmargin: 0 auto}
.grid >li { width: 285pxheight: 500pxoverflow: hiddenfloat: leftmargin: 20px 0 20px 30pxposition: relative}
.grid >li:hover {box-shadow: 0 0 15px 0 rgba(0, 0, 0, 0.5)}
.grid>li section {position: relativetransition: all 0.25swidth: 100%}
.grid>li h2 {font: bold 14px montserratcolor: #ffftext-transform: uppercaseposition: absolutetext-align: centerwidth: 60%left: 20%top: 100pxpadding: 10px 0border: 2px solid whiteborder-radius: 4px}
.sidenav { position: absolutetop: 0left: 0bottom: 0background: linear-gradient(rgba(50,60,60, 1), rgba(50,60,60, 0.7))width: 50pxtransition: all 0.25soverflow: hiddenpadding-top: 100px}
.sidenav li { _overflow: hiddenwidth: 150px}
.sidenav a { text-decoration: nonecolor: #eee display: blockline-height: 48px }
.sidenav span {display: block}
.sidenav b { padding-left 10pxdisplay: blockcolor: whitefont-family: Montserratfont-size: 12pxline-height: 4opacity: 0}
.sidenav a i { display: blockfloat: leftfont-size: 16pxline-height: 48pxwidth: 50pxtext-align: center}
/*All instances*/
.grid>li:hover .sidenav {width: 150px}
.grid>li:hover section {margin-left: 150px}
.grid>li:hover b {opacity: 1}
.sidenav li:nth-child(1) b, .sidenav li:nth-child(1) a {transition-delay: .08s}
.sidenav li:nth-child(2) b, .sidenav li:nth-child(2) a {transition-delay: .16s}
.sidenav li:nth-child(3) b, .sidenav li:nth-child(3) a {transition-delay: .24s}
.sidenav li:nth-child(4) b, .sidenav li:nth-child(4) a {transition-delay: .32s}
.sidenav li:nth-child(5) b, .sidenav li:nth-child(5) a {transition-delay: .40s}
.sidenav li:nth-child(6) b, .sidenav li:nth-child(6) a {transition-delay: .48s}
/*Three*/
.three .w {transform: perspective(100px) translateZ(-24px)}
.three b {transform: perspective(100px) rotateY(180deg) translateZ(24px) scale(0.5)}
.three:hover b {transform: perspective(100px) rotateY(0) translateZ(24px) scale(1)transition: all 0.8s cubic-bezier(0.175, 0.885, 0.32, 1.275)background: transparent}
.three .sidenav {width: 150px}
/*Two*/
.two .w {transform: perspective(100px) translateZ(-24px)}
.two b {transform: perspective(100px) rotateX(90deg) translateZ(24px) scale(1.5)opacity: 0}
.two:hover b {transform: perspective(100px) rotateX(0) translateZ(24px) scale(1)transition: all .4sopacity: 1}
.two .sidenav {width: 150px}
/*One*/
.one .w {transform: perspective(100px)}
.one b {transform: perspective(100px) rotateY(90deg)_opacity: 0transform-origin: left center_border: 1px solid white}
.one:hover b {transform: perspective(100px) rotateX(0)transition: all .4sopacity: 1}
.one .sidenav {width: 150px}
.one .sidenav span {float: leftwidth: 100px}
</style>
<!--[if IE]>
<script src="http://libs.useso.com/js/html5shiv/3.7/html5shiv.min.js"></script>
<![endif]-->
</head>
<body>
<div class="htmleaf-container">
<header class="htmleaf-header bgcolor-11">
<div class="htmleaf-demo center">
<a href="index.html">DEMO1</a>
<a href="index2.html" class="current">DEMO2</a>
<a href="index3.html">DEMO3</a>
<a href="index4.html">DEMO4</a>
</div>
<div style="text-align:centerclear:both">
<script src="/gg_bd_ad_720x90.js" type="text/javascript"></script>
<script src="/follow.js" type="text/javascript"></script>
</div>
</header>
<div class="htmleaf-content bgcolor-8">
<ul class="grid">
<li class="one">
<ul class="sidenav">
<li><a><i class="fa fa-check"></i><span class="w"><b>Tasks</b></span></a></li>
<li><a><i class="fa fa-inbox"></i><span class="w"><b>Messages</b></span></a></li>
<li><a><i class="fa fa-pencil"></i><span class="w"><b>New Post</b></span></a></li>
<li><a><i class="fa fa-cog"></i><span class="w"><b>Settings</b></span></a></li>
<li><a><i class="fa fa-star"></i><span class="w"><b>Starred</b></span></a></li>
<li><a><i class="fa fa-power-off"></i><span class="w"><b>Logout</b></span></a></li>
</ul>
<section>
<h2>Door Opening</h2>
<img src="img/mb1.png"/>
</section>
</li>
<li class="two">
<ul class="sidenav">
<li><a><i class="fa fa-check"></i><span class="w"><b>Tasks</b></span></a></li>
<li><a><i class="fa fa-inbox"></i><span class="w"><b>Messages</b></span></a></li>
<li><a><i class="fa fa-pencil"></i><span class="w"><b>New Post</b></span></a></li>
<li><a><i class="fa fa-cog"></i><span class="w"><b>Settings</b></span></a></li>
<li><a><i class="fa fa-star"></i><span class="w"><b>Starred</b></span></a></li>
<li><a><i class="fa fa-power-off"></i><span class="w"><b>Logout</b></span></a></li>
</ul>
<section>
<h2>Flip Down</h2>
<img src="img/mb2.png"/>
</section>
</li>
<li class="three">
<ul class="sidenav">
<li><a><i class="fa fa-check"></i><span class="w"><b>Tasks</b></span></a></li>
<li><a><i class="fa fa-inbox"></i><span class="w"><b>Messages</b></span></a></li>
<li><a><i class="fa fa-pencil"></i><span class="w"><b>New Post</b></span></a></li>
<li><a><i class="fa fa-cog"></i><span class="w"><b>Settings</b></span></a></li>
<li><a><i class="fa fa-star"></i><span class="w"><b>Starred</b></span></a></li>
<li><a><i class="fa fa-power-off"></i><span class="w"><b>Logout</b></span></a></li>
</ul>
1，一般下拉菜单的二级菜单都是绝对定位的，绝对定位的元素脱离了常规流，所以不占位，他们会叠加在其他元素的上面或者下面2，你可以把这里面的空格当作［内］，也就是子孙元素的意思
#menu ul li ---- #menu 内的 ul 内的 li
#menu ul li:first-child a:hover:after ---- #menu 内的 ul 内的 li(并且是ul的第一个子元素) 内的 a 鼠标指向时 after
after/before 的意义在于，他们不存在在html文档中，但是又能被浏览器显示出来，因此，可以用来实现一些效果。
常用的例如：
～文字前面的icon，不用在html中插入多余的空元素，直接使用after或者before，前面后面随便插.......
～清除浮动
～为引用的文字加入引号
～画一些有意思的图标
