What should I be putting in the code nothing I put is working

Tell us what’s happening:
Describe your issue in detail here.

  **Your code so far**

<style>
:root {
  --red-color: red;
}
.red-box {
  color: red;
  background: var(--red-color);
  height: 200px;
  width:200px;
}
</style>
<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/96.0.4664.110 Safari/537.36

Challenge: Improve Compatibility with Browser Fallbacks

Link to the challenge:

The instructions want you to add a fallback for the background color. I don’t think the color property is the same thing.