Expected RBRACE at line 16 col 1

Before I share my problem, I just wanna say that I am new to CSS, I only started trying to help my problems in my website code dissapear but it doesn’t work.

Anyways, I own a wiki in FANDOM, I am trying to improve the design by using Developer CSSes on the MediaWiki:Common.css and so far, it is good, but I have noticed that the most recent CSSes I have put in the page don’t work, I checked the first one that did not work and I fixed the problem where the RBRACE at the end of the script did not work.

But then, I was encountered with another problem, the “FALLBACK BACKGROUND” problem, I entered the “// fallback color” before the “background” line as requested by a Google result, but then I encountered the problem I am on right now.

“Expected RBRACE at line 16, col 1.”

I tried everything, but it would not work, that is why I am requesting help here.

My code:

.WikiaBarWrapper, #WikiaBarWrapper .wikia-bar, .WikiaBarWrapper .toolbar {
// fallback color
background: rgba(0, 0, 0, 0.3);

Hey @digital1717814103, welcome to the forums!

Question, why are you mentioning the same class twice? Also, are all these classes with one class? If not, why are there no commas?