Vector Pinball (also available on f-droid) is a pretty decent pinball game. Very lightweight, free, no ads.

Also Vodobanko (not free) for a hostage rescue type game. There’s a free version too if you want to try before you buy.

There’s https://bunny.net/fonts/ - basically Google fonts without the Google.

I had this problem, and it was definitely a theme issue.

https://askubuntu.com/a/1372318 may be helpful in setting a theme just for libreoffice, it you’re using GTK themes. (Basically, override the GTK_THEME variable in the .desktop file). I haven’t tried it myself since I just switched to a different theme.