Modern dialog and form UX design. Meaning, buttons should be right-justified, and the affirmative action should be the right-most button.
Example: A dialog that says "Are you sure you want to delete this thing?", it should have two buttons, right justified, that state [Cancel] and [Delete], rather than [Delete] [Cancel] or [Yes] [No] since "Delete" is the affirmative action and using yes and no can be vague. You want actions to convey their intent clearly and deliberately.
It's nitpicky, but every time I hit cancel on something because it's the right most button, particularly on mobile, it makes me want to die a little.