Default fonts for ubuntu-MATE

Hey guys, I have been playing with font combos in my theme. I took this formula form Pop!_OS and it really does make a nice change to readability and the look of everything. I thought it may be something worth considering that would be fairly easy to change and may make a big difference in appearance of the distro in general.

Window Titles: Fira Sans SemiBold 10

Interface: Fira Sans Book 10

Documents: Roboto Slab Regular 11

Monospace: Fira Mono Regular 11

So how would a novice try? I found the fonts online and installed using Mate Font Viewer. I opened Mate Tweak/Windows/Fonts. I see Window Titles and Documents. I don't see Interface or Monospace.

I did it in appearance settings

Thanks for the visual. Same place, I just did not understand description.

There is a script I found online to install the fira fonts.
At the repositories I found only the fira code.

There is a ppa here where you can get them all also. ..

I think that the default (Ubuntu) is legible enough. Personally, I like Cabin as san-serif and Iosveka for monospace better, but Fira Sans is good too!