docs: def condense_multidimensional_zeros(css):
      """Replace `:0 0 0 0;`, `:0 0 0;` etc. with `:0;`."""
  
      css = css.replace(":0 0 0 0;", ":0;")
      css = css.replace(":0 0 0;", ":0;")
      css = css.replace(":0 0;", ":0;")
  
      # Revert `background-position:0;` to the valid `background-position:0 0;`.
      css = css.replace("background-position:0;", "background-position:0 0;")
  
      return css