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

HTML-CSS
1

Tell us what’s happening:

Your code so far


<style>
  :root {
    --red-color: red;
  }
  .background{
    backgroundcolor: red;
  }
  .red-box {
    
    background: var(--red-color, red);
    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/70.0.3538.77 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/responsive-web-design/basic-css/improve-compatibility-with-browser-fallbacks

2

You don’t need this style.

Simply give background:red to the line above background with css variable.