Basic CSS: Improve Compatibility with Browser Fallbacks

Basic CSS: Improve Compatibility with Browser Fallbacks


I added red to the background and it is not working. I tried doing it in different browsers (IE, Firefox, and Chrome).

	:root {
		--red-color: red;

	.red-box {

		background: var(--red-color, red);
		height: 200px;
		width: 200px;
<div class="red-box"></div>type or paste code here

Css Improve compatibility

Hi there froxas908, i had the same problem. Carefully read the instructions before you try it:

Your .red-box rule should include a fallback with the background set to red immediately before the existing background declaration.

When you put it like this: “background: var(–red-color);” you are not reading the instructions. It says “before” the existing background declaration. So the answer will be:

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


thank you :slight_smile:


I had the same mistake, thank you so much!


This is a fallback in case the browser doesn’t support custom properties (variables).

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

This is a custom property fallback value in case the given variable is not yet defined.

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


thanks :sunglasses::sunglasses: been getting this wrong for like …:japanese_goblin:


Thank you i fall in the same mistake xD


wtf:joy: thank you omg


I think “improve-compatibility-with-browser-fallbacks” is again broken.
Can anyone confirm?
PS : i can’t yet post the links


Why do you think is broken?
If you use the “Ask for help” button inside the challenge you will create a forum post that has already your code formatted in it
Or just copy your code here using the </> button in the post editor to format you code


i had the same problem also, Thank you :smiley:


Yes it is!! been stuck for a few hours, looking for the right answers from this forum…but none of the answers did not work :confused:


Thanks. i have this problem now but with your comment, i have been able to solve the background issue.

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

and still not working  --' 


It is not working tried everything possible;;;.


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


You have changed the existing css rule, that may be the issue