N/M re: zoom level indicator...never realized it is combo of level indicator and reset button.
And the suggested outline treatment is just one of multiple ways of meeting Working Drafts:
I find Figure 17 in the former a particularly useful example for round controls.
It uses far more padding than 2px...basically to get up to recommended 44px X 44px touch-friendly target sizes.
It's also applicable to not necessarily round controls, e.g. radios, checkboxes, switches, chevron buttons, off-page link indications, etc.
Another (sort-of) open-source browser (which will remain unnamed) uses this extensively in its Settings UI, for example (though not in its main app menu's zoom controls, at this point in time).
Apologies if this has all been considered already.