Css browser compability fall back

someone please explain this tworkingo me.havebtried solving it but not

  **Your code so far**

<style>
:root {
  --red-color: red;
}

.red-box {
  backgroun: red; 
  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 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36

Challenge: Improve Compatibility with Browser Fallbacks

Link to the challenge:

You spelled “background” incorrectly.

oh,thanks
,thanks alot