Improve Compatibility with Browser Fallbacks( Pls Help!)

Tell us what’s happening:
Hi, Kindly provide solution to this code. I’m stuck

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 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36.

Link to the challenge:

How would you declare background color if you didn’t know about variables? That is what a browser that doesn’t know variables needs

Thank you. I’ve been able to resolve this.
I just background color to red. in case variable do not work