Keyboard navigation
Being able to run the whole interface with just Tab, arrows, Enter, and Escape, with no mouse or trackpad involved.
See it
What it is
Keyboard navigation means every action in the interface is reachable and operable with keys alone. Tab and Shift+Tab move between controls, and then each control has its own activation key: links fire on Enter, buttons on Enter or Space. Composite widgets (menus, tabs, sliders, listboxes) take arrow keys, plus Home and End, in whatever combination the ARIA pattern for that widget specifies, and Escape backs out of surfaces built to be dismissed. It is the baseline that screen reader users, switch users, voice control users, and anyone with a temporarily broken wrist all depend on.
The rule of thumb from the ARIA authoring practices: Tab moves between components, arrows move within one. A tab list is a single stop; the arrows pick the tab. That pattern is called roving tabindex, and it keeps a 40-item menu from costing 40 presses. Native elements give you most of this free, which is the cheapest reason to use them.
Two things that break it constantly. Click handlers on div and span: they are not focusable and Enter does nothing, so the feature simply does not exist without a mouse. And positive tabindex values (tabindex of 3), which yank those elements to the front of the entire page's tab order and scramble everything else. Use tabindex='0' to add a stop, tabindex='-1' for programmatic focus only, and nothing higher.
Ask AI for it
Make this interface fully keyboard operable. Replace click-handling divs and spans with real button and a elements so the native keys come free: Enter on links, Enter or Space on buttons. Ensure Tab reaches every control in an order that matches the reading order. For each composite widget (tabs, menus, listboxes, toolbars), follow the matching ARIA Authoring Practices pattern and implement that pattern's specific arrow, Home, and End keys with roving tabindex, rather than assuming one key set fits every widget. Wire Escape only where there is something dismissible to dismiss (dialogs, popovers, open menus). Remove any positive tabindex values. Then list the full key sequence a user presses to complete the primary task, naming the pattern you followed for each widget.