/* https://online-free-tools.com/fr/css_generateur_motif_pattern_background */

.demo{
  background: linear-gradient(45deg, #00f 12.5%, #fff 12.5%, #fff 37.5%, #00f 37.5%, #00f 62.5%, #fff 62.5%, #fff 87.5%, #00f 87.5%);
  background-size: 100px 100px;
  background-position: 50px 50px;
}