How do you make sure the interfaces you build are accessible, and have you ever had to argue for it?

Split it into what you do by default and what you check.

By default: semantic HTML before ARIA — a real <button> is keyboard-operable, focusable, and announced correctly with no extra work, while a <div onclick> needs four attributes and a key handler to catch up. Labels tied to inputs, headings in order, alt text that says what the image is for, and visible focus styles you never remove.

What you check:

• Tab through the whole feature without touching the mouse.
• Run axe or Lighthouse, understanding that automated tools catch perhaps a third of real problems.
• Test one flow with a screen reader — VoiceOver or NVDA.
• Check colour contrast at design time.

On arguing for it: the effective arguments are legal exposure, the size of the affected audience, and the fact that retrofitting costs several times more than building it in. The ineffective argument is that it is the right thing to do — true, but it rarely moves a roadmap on its own.