Improve Compatibility with Browser Fallbacks--HELP!

Tell us what’s happening:
I’m supposed to improve the browser compatibility of the code by adding another background declaration right before the existing declaration and set its value to red. I feel like I have tried every possibility so not sure what I’m doing wrong here.

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 (Macintosh; Intel Mac OS X 10_10_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36.

Link to the challenge:

This is the starting code

What are the things you tried?

I tried this (within .red-box)

background: var(red, --red-color); and background: var(–red-color, red); AND
background: red, var(–red-color);

You shouldn’t touch the existing background rule
You need a different background rule above that in case the browser can’t read variables

In practice having both a variable fallback and a browser fallback is good, right now instead you shouldn’t change the code that’s already there

Thank you! That helps.