why is linear gradient repeating code example

Example 1: css color gradient background full height

html {
    height: 100%;
}
body {
    height: 100%;
    margin: 0;
    background-repeat: no-repeat;
    background-attachment: fixed;
}

Example 2: repeating-linear-gradient

body {
  background-image: repeating-linear-gradient(-45deg,
      transparent,
      transparent 20px,
      black 20px,
      black 40px);
  /* with multiple color stop lengths */
  background-image: repeating-linear-gradient(-45deg, 
      transparent 0 20px, 
      black 20px 40px);
}