width: 0px;
height: 0px;
border-left: 5px solid transparent;
border-right: 5px solid transparent;
border-bottom: 5px solid#2f2f2f;
}
div#down {
width: 0px;
height: 0px;
border-left: 20px solid transparent;
border-right: 20px solidtransparent;
border-top: 20px solid #f00;
}
div#left {
width: 0px;
height: 0px;
border-top: 10px solid transparent;
border-bottom: 10px solid transparent;
border-right: 10px solidyellow;
}
div#right {
width: 0px;
height: 0px;
border-top: 60px solid transparent;
border-bottom: 60px solid transparent;
border-left: 60px solid green;
}
html:
<div id="up"></div>
<div id="down"></div>
<div id="left"></div>
<div id="right"></div>