Creating Triangles in CSS

Little people realize when a browser draws the borders, it draws them at angles. This technique takes advantage of that. One side of the border is colored for the color of the arrow, and the rest are transparent. Then you set the width of the border to something large, the ones above are 40px. To demonstrate here is a div with all sides colored.

HTML

<div class="css-arrow-multicolor">
</div>

CSS

.css-arrow-multicolor {
  border-color: red green blue orange;
  border-style:solid;
  border-width:40px;
  width:0;
  height:0;
}

As you can see there are triangles hidden in that square. These triangles are right triangles with a little tweaking with the border sizes you can get acute triangles.

CSS

.css-arrow-acute {
  border-color: red green blue orange;
  border-style:solid;
  border-width:25px 10px 15px 30px;
  width:0;
  height:0;
}

With a little creativity and tweaking there are lots of shapes that can be made.

border-style:dotted;	border-style:dashed;	border-style:outset;	border-style:inset;
border-style:ridge;	border-style:groove;	border-style:double;

Never thought about doing this with CSS!? Amazing isn't it!