TASK: Improve Compatibility with Browser Fallbacks

Tell us what’s happening:
I don’t understand what I have to do

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 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36.

Link to the challenge:

You need to add this above already defined background

background: red;

Not all browsers support variables, so you need to have a fallback option