One of the surprising—and surprisingly useful—things you can do with CSS is build triangles. That’s right: rather than crafting a triangle PNG file using a graphics program, you can create a triangle of practically any shape, size, and orientation just by manipulating a few border-related CSS properties on a block-level element. Wait: border properties!? Yep. It’s more than a little strange and counter-intuitive at first, so let me take you through the steps.