Example picture can be found here.
http://forums.codeblocks.org/index.php?topic=22405.0
Example of a WxWidgets program using tabs that are displaying properly:
https://github.com/wxWidgets/wxWidgets/blob/master/samples/taborder/taborder.cpp
Codeblocks currently uses some weird abominations instead of native GtkNotebook widgets that are displayed as wxPizza in GTK interactive debugger. I have no idea what do they do but i don't think there is a reason why they should be used instead of whatever is used in the program above.
Oh ok, i've got it, it's all about wxAuiNotebook, its art providers are pretty ugly. At least correct the simple art provider so that it doesn't show white tabs and black text on dark GTK themes.
Same applies to zone headers, e.g. "management", "logs & others"... black text on black background = no good
Last edit: TSM 2018-08-16
Unfortunately I couldn't find a GTK 3 api to draw notebooks manually, so what we're doing for GTK 2 won't be possible for GTK 3.
We'll have to provide a better notebook for sure. I'm not sure when it will happen.
I'm not really a fan of GTK 3 and I don't spend any time testing it. For some unknown reason everything is so big in GTK3. Ugly...
What is wxPizza?
I have no idea what is it. I guess that's some GTK widget that is used by Wx to draw its own stuff there. You can see it in interactive GTK3 debugger if you select tab area of AuiNotebook or some other element, not sure which exactly.