CSS gradient checkerboard pattern

It's 2020 and this can now be created with a single CSS gradient (if you don't need to support IE/ pre-Chromium Edge).

html {
  background: repeating-conic-gradient(#808080 0% 25%, transparent 0% 50%) 
              50% / 20px 20px
}

I wrote a detailed explanation on CSS Tricks for how this works.

Just modify the background-position like in the below snippet to get the required output. This works fine in Firefox, Chrome, Opera, IE11 and Edge.

body {
  background-image: linear-gradient(45deg, #808080 25%, transparent 25%), linear-gradient(-45deg, #808080 25%, transparent 25%), linear-gradient(45deg, transparent 75%, #808080 75%), linear-gradient(-45deg, transparent 75%, #808080 75%);
  background-size: 20px 20px;
  background-position: 0 0, 0 10px, 10px -10px, -10px 0px;
}

The problem seems to be happening because of a difference in the way the angles are handled by the -moz linear gradient and the standard one. -45deg in the -moz linear gradient seems to be equal to 135deg in the standard gradient (but changing the angle is resulting in a strange dot in the middle).

The below screenshots show the difference (both taken in the latest Firefox v44.0).

Output with -moz-linear-gradient:

Output with linear gradient: