mysticsymbolic.github.io/lib/pages/vocabulary-page.css

.checkerboard-bg {
  /* https://codepen.io/pascalvgaal/pen/jPXPNP/ */
  background: #eee
    url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" width="400" height="400" fill-opacity=".1" ><rect x="200" width="200" height="200" /><rect y="200" width="200" height="200" /></svg>');
  background-size: 20px 20px;
}