body {
  background-image: linear-gradient(45deg, transparent 20%, black 25%, transparent 25%), 
                    linear-gradient(-45deg, transparent 20%, black 25%, transparent 25%), 
                    linear-gradient(-45deg, transparent 75%, black 80%, transparent 0),
                    radial-gradient(gray 2px, transparent 0);
  background-size: 30px 30px, 30px 30px;
}

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