New Browser Fallbacks in CSS Section

Going back through CSS curriculum I found this new exercise that makes no sense to me in it’s context.

I cannot recall reading anything about :root or var in The CSS section. Can anyone advise me where to find this info?

https://learn.freecodecamp.org/responsive-web-design/basic-css/improve-compatibility-with-browser-fallbacks

the answer seems to be in the following exercises. Makes me wonder if these are updates or I simply forgot them.

It depends on when the last time you did this section was. A lot of content was added in the last year.

I completed the content about a year ago and recently came back to find there were a few new lessons added yes.

There has been a TON added in the last year. Feel free to skip any topics that you already feel you know well. There’s no need to go back if you don’t want to.