$black-alpha: rgba(0, 0, 0, 0.3);
$black-alpha-2: rgba(0, 0, 0, 0.4);

body {
  background-color: $black-alpha;
  background-image: linear-gradient(45deg, $black-alpha 24%, $black-alpha-2 25%, $black-alpha-2 26%, $black-alpha 26%, $black-alpha 74%, $black-alpha-2 75%, $black-alpha-2 76%, $black-alpha 76%), 
  linear-gradient(-45deg, $black-alpha 24%, $black-alpha-2 25%, $black-alpha-2 26%, $black-alpha 26%, $black-alpha 74%, $black-alpha-2 75%, $black-alpha-2 76%, $black-alpha 76%);
  background-size: 100px 100px;
}

External CSS

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External JavaScript

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