Change background colors in different categories

Hi, I am working with Codium Grid and try to change the color of each main category: Blogs, Boeken etc.
I put a custom css code to Blogs in my menu with screenfunctions and named it: blogsbckgr
Then I went to my CSS stylesheet and added: ‘ .blogsbckgr {
background-color: #00d8ff; ‘

I also tried to do it with the category id, which is 830, but that doesn’t work either.

What am I doing wrong here?
https://www.marcelineke.nl
Thanks upfront.