css小三角

 

 

<div id="demo"></div>
<style>
#demo {
width: 100px;
height: 100px;
background-color: #ccc;
position: relative;
border: 4px solid #333;
}

#demo:after,
#demo:before {
border: solid transparent;
content: ' ';
height: 0;
left: 100%;
position: absolute;
width: 0;
}

#demo:after {
border-width: 9px;
border-top-color: #ccc;
bottom: -18px;
left: 38px;
}

#demo:before {
border-width: 14px;
border-top-color: #333;
bottom: -28px;
left: 33px;
}
</style>