CSS3 implements mouse hover to display expanded content

    <p id="nav">   
       <a id="nav-main"><span><i class="icon-home"></i> 主界面</span></a>   
         <a id="nav-sum"><span><i class="icon-laptop"></i> 统计界面</span></a>   
   </p>    
CSS代码：   
/*******************************************************************************/
/*********************************** nav **************************************/
/*******************************************************************************/
#nav{   
    box-sizing:border-box;   
    width:200px;   
    height:100%;   
    position:fixed;   
    padding-top:80px;   
}   
#nav a{   
    display:block;   
    width:30px;   
    height:52px;   
    position:relative;   
    margin-top:50px;   
}   
#nav a span{   
    display:inline-block;   
    width:46px;   
    height:50px;   
    font-size:1em;   
    font-weight:600;   
    color:rgba(255,255,255,0.9);   
    text-indent:3px;   
    line-height:52px;   
    cursor:pointer;   
    overflow:hidden;   
}   
#nav a span i{   
    font-size:1.3em;   
}   
#nav a::after{   
    content:&#39;&#39;;   
    display:block;   
    width:0;   
    height:0;   
    position:absolute;   
    rightright:-32px;   
    bottombottom:0;   
    border-top:26px solid transparent;   
    border-right:16px solid transparent;   
    border-bottom:26px solid transparent;   
}   
#nav-main{   
    background-color:rgb(211,83,80);   
}   
#nav-sum{   
    background-color:rgb(0,158,163);   
}   
#nav-main::after{   
    border-left:16px solid rgb(211,83,80);   
}   
#nav-sum::after{   
    border-left:16px solid rgb(0,158,163);   
}   
#nav a:hover{   
    -webkit-animation:extend-a 0.5s;   
    -moz-animation:extend-a 0.5s;   
    animation:extend-a 0.5s;   
    width:100px;   
}   
#nav a span:hover{   
    -webkit-animation:extend-span 0.5s;   
    -moz-animation:extend-span 0.5s;   
    animation:extend-span 0.5s;   
    width:116px;   
}   
/******************* a扩展效果 ******************/
@-webkit-keyframes extend-a{   
    0% {   
        width:30px;   
    }   
    100% {   
        width:100px;   
    }   
}   
@-moz-keyframes extend-a{   
    0% {   
        width:30px;   
    }   
    100% {   
        width:100px;   
    }   
}   
@keyframes extend-a{   
    0% {   
        width:30px;   
    }   
    100% {   
        width:100px;   
    }   
}   
/******************* span扩展效果 ******************/
@-webkit-keyframes extend-span{   
    0% {   
        width:46px;   
    }   
    100% {   
        width:116px;   
    }   
}   
@-moz-keyframes extend-span{   
    0% {   
        width:46px;   
    }   
    100% {   
        width:116px;   
    }   
}   
@keyframes extend-span{   
    0% {   
        width:46px;   
    }   
    100% {   
        width:116px;   
    }   
}