C::B + wxGTK3 is broken, because none of the developers is using it actively, yet, as far as I know.
You can see the known problems here
https://sourceforge.net/p/codeblocks/tickets/search/?q=labels:%22gtk3%22 (just two, but I'm pretty sure there are plenty more).
If you're on hidpi monitor, wxgtk3 would feel especially broken if you're not running something which is very recent wx-master.
GTK+3 is fine as working, but Gnome people are not my favourites to say it politely.
p.s. the tabs are broken. GTK3 makes it impossible to replicate its themed tabs, as we're doing in gtk2
p.p.s. the editor is configurable you can make it dark.