How could include a fallback with the background set to red immediately?

HTML-CSS
#1

How could include a fallback with the background set to red immediately ?
Thank you!

My code so far


<style>
  :root {
    --red-color: red;
  }
  .red-box {
    
    background: var(--red-color,red);
    height: 200px;
    width:200px;
  }
</style>
<div class="red-box"></div>
#2

you have written a fallback for the case in which the variable doesn’t have a valid value, you need a fallback for when the browser doesn’t use variables, so you need a different css rule for the background that doesn’t use variables

#3

I just passed the test!

my solution is below:

:root { --red-color: red; } .red-box { background:red; background: var(--red-color); height: 200px; width:200px; }
#4