You arent going to be able to style a native UI with the same amount of customisation as you would a composite (drawn) UI - its just not feasible, in fact, wxWidgets on OSX is extremely limited with regards to customization as the UI it creates is 100% native - and OSX is VERY limited it what it allows UI to “do”.
This isnt really a limitation of haxeui-hxwidgets, or wxWidgets really, its that the UI is native and therefore is limited by native apis - qt will allow alot of more customization as its not actually a native UI, it just looks like it is but its actually custom drawn (but using OS hooks and done very well). There is a hxQt and a haxeui-qt, but they are highly experimental at this stage.
If you want a 100% consistent UI across OS’s then you’ll have to use a composite backend (like html5, or openfl, or kha) - but obviously this wont be native anymore and things may feel “out of place” (for example scrollbars)
It might make more sense if you try to explain what you are trying to do… for example, if you are interested in a native UI, why are you looking to change the background colour on hover? (which will absolutely NOT work in haxeui-hxwidgets when targeting OSX anyway)
slice-9 isnt implemented on haxeui-hxwidgets - which is what the kenney theme runs off of essentially - this is because i got some really bad “flashing” with the components - i might have another go at it, as i have some ideas. But again, if you are trying to theme a native application with something as drastic as the kenney theme then why not use a composite backend? It seems using a native UI and then trying to “paint” it as a totally NON native ui seems strange.
PS: ill checkout the date thing.