The lemming sprites look very nice!
The button panels aren't particularly useful though, as they don't fit with how NL works. Take a look in styles/default/panel - notice how we have skill_panels.png that contains a few panel backgrounds (this basically works by using the first one for the first panel, second for the 2nd, etc, if it runs out, it loops back to the first one for the next panel), and then icon graphics such as icon_restart.png that just have the icon graphic with a blank background.
With skill icons (except Disarmer, which currently works the same way as above, but this will likely change once we have a proper disarmer sprite), this goes one step further: only the background gets used. The actual icon itself is generated using the lemming sprite. (This is a new thing in recent versions of NL.)
As it looks like there's serious interest in making this happen, and not just tossing around of "this would be a neat idea, right?", I'll give some strong consideration to getting these into use once V12.7 doesn't need much more work, and maybe even having the feature ready for V12.8 (although
no promises here, and if it misses that, it'll be V12.10, as
only even-numbered updates make major graphical changes from V12.8 onwards). To content creators - don't panic, the use of high-res graphics will be completely optional, and you can continue shipping styles with only low-res graphics (indeed, I likely won't update my existing ones to high-res); you'll just have the ability to
also ship high-res graphics for those who want to use them. We'll discuss closer to the time whether it's "you must provide low-res" or "you can provide just high-res, and NL will downscale".