Improve Compatibility with Browser Fallbacks122

Tell us what’s happening:
what should I do?

Your code so far

  :root {
    --red-color: red;
  .red-box {
    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/70.0.3538.102 Safari/537.36 OPR/57.0.3098.116.

Link to the challenge:

You need to not change the existing code
And add a fallback for when a browser doesn’t use variables, so a css rule for the background color in the usual way