Rule should include a fallback with the background

Good Day.
I know this is a small issue but not for me i’ve been stuck for about a week. if anyone can help

Your code so far


<style>
  :root {
    --red-color: red;
  }
  .red-box {
    
    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/76.0.3809.132 Safari/537.36.

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

background: red;
background: var(–red-color);

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