Your .red-box rule should include a fallback with the background set to red immediately before the existing background declaration?

[ChrisCline1138]

Refer to this post as it deals with the same problem

Improve Compatibility with Browser Fallbacks help!

Tell us what’s happening: hey guys! I got a problem over here, I don’t know how to improve the browser compatibility by adding another background declaration right before the existing declaration. It has to be red! THANKS FOR HELPING! MUCH LOVE! Your code so far <style> :root { --red-color: red; } } .red-box { background: var(--red-color); height: 900px; width:500px; } </style> <div class="red-box"></div> Your browser information: User Agent is: Mozilla…