CodePen Embed - 3x3 blueprint CSS pattern

body {
  background-size: 72px 72px, 72px 72px, 24px 24px, 24px 24px;
  background-image: linear-gradient(rgba(0, 0, 0, .5) 2px, transparent 2px), linear-gradient(90deg, rgba(0, 0, 0, .5) 2px, transparent 2px), linear-gradient(rgba(0, 0, 0, .28) 1px, transparent 1px), linear-gradient(90deg, rgba(0, 0, 0, .28) 1px, transparent 1px);
  background-position: -2px -2px, -2px -2px, -1px -1px, -1px -1px;
}

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