Making Triangles with CSS3

css-only triangles! yay!

Demo

Markup

<div class="arrow-up"></div>
<div class="arrow-down"></div>
<div class="arrow-left"></div>
<div class="arrow-right"></div>

CSS

.arrow-up {
	width: 0;
	height: 0;
	border-left: 5px solid transparent;
	border-right: 5px solid transparent;
 
	border-bottom: 5px solid black;
}
 
.arrow-down {
	width: 0;
	height: 0;
	border-left: 20px solid transparent;
	border-right: 20px solid transparent;
 
	border-top: 20px solid #f00;
}
 
.arrow-right {
	width: 0;
	height: 0;
	border-top: 60px solid transparent;
	border-bottom: 60px solid transparent;
 
	border-left: 60px solid green;
}
 
.arrow-left {
	width: 0;
	height: 0;
	border-top: 10px solid transparent;
	border-bottom: 10px solid transparent; 
 
	border-right:10px solid blue;
}

Source