Why Improve Compatibility with Browser Fallbacks

Tell us what’s happening:

I just do not get it

Your code so far

  :root { 
    --red-color: red;
  .red-box {

    background: --red-color: red;
    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/70.0.3538.102 Safari/537.36.

Link to the challenge:

you just need to set the first background color to red as its a fallback color for if the variable fails