What does this button on the back of my case do?

[Ohainexo]

Hey mates,
I haven't built a PC before an I am on my first non-prebuilt computer and I was wondering what this button did - Click here to see

I personally don't know as I didn't have a button like that on my prebuilt PC. Thanks mates in advance for any help.

 

[Ohainexo]

Nevermind mates, found the answer. Thanks to the suggestions on the forums that link you to similar posts.

 

[Ohainexo]

Due to the suggestions from the forum, I found out it is to light up the top 200mm fan.