Browser fallback does not recognize background-color

Can you please tell me why I am getting an error?

Your code so far

  :root {
    --red-color: red;
  .red-box {
    background-color: red;
    background: var(--red-color);
    height: 200px;
<div class="red-box"></div>

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.80 Safari/537.36.

Link to the challenge:

it is correct in general, but this challenge expect you to use the same rule used in the rule with variable, so just background, it is a short-hand for the background-color rule