What I've done
The site aims to meet the Web Content Accessibility Guidelines (WCAG) 2.2 at level AA. In practice, that means:
proper semantic HTML, with headings in a logical order and clear page landmarks
everything can be reached and used with a keyboard, with a visible focus outline
text and background colours chosen for good contrast
descriptive alternative text on meaningful images
form fields with clear labels and helpful error messages
a layout that adapts to different screen sizes and zooms up to 400% without losing content
respecting your device's reduced motion setting