- Open ULS, Display Settings.
- Change language to English and font to Opendyslexic.
- Notice that Apply Cancel buttons remain in system font.
Oops, press "Save" before completing.
Basically, I tried to clean-up the font settings in the CSS for the panel, but no matter what I did, the font wasn't actually applied to the buttons. Dev tools in both Firefox and Chrome identified that the webfont is supposed to be applied, but didn't actually apply it.