The simple theme should implement the ARIA recommendations.

Here some items & links that can help to the basic steps:

• https://developer.mozilla.org/en-US/docs/Tools/Accessibility_inspector
• https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/
• on a google.com result page, press tab various accessibility links including "skip to content": https://css-tricks.com/how-to-create-a-skip-to-content-link/
• the preferences, engine tab should have a "disable all engines" / "enable all engines" (in the tab, not globally)

Some of the issues:

• The tabs, the categories and the checkboxes (in the preferences) can't get the focus ( display: none must be replaced by appearance: none):
  • checkbox: https://codepen.io/dalf-the-encoder/pen/VwrQKKm
  • tabs
• Simple theme has inverted checkboxes #1316