css shapes - How to make half-square background in css

Question

Is it possible to make in pure css background for half square like on the image. I know that it can be done with an image as background, but I need to use 5 different colours, and maybe in future the colours can be changed.

Answer 1

If your divs have fixed sizes, you can use borders to make two triangles as described in How do CSS triangles work?:

div{
  display:inline-block;
  border-top:100px solid red;
  border-right:100px solid grey;
  }

<div></div>