The following button styles differ between OOjs UI and mediawiki UI:
[x] constructive, destructive, progressive buttons
[ ] frameless constructive, destructive, progressive buttons - both need to be changed
[ ] default button sizes
[ ] button hover effects (border change)
[x] disabled buttons - The disabled buttons in OOJS UI are difficult to read. They should probably adopt mediawiki-ui's disabled style.
[ ] standalone icon buttons - much smaller in OOJS UI, we probably need two different size options, as mobile needs larger icons.