What you need to know
A navigation menu is a core route to the site. If it works only with a mouse, keyboard users may be blocked from every page or lose their place when a panel opens.
How to apply it
Use native links and buttons, keep focus order predictable, expose expanded state on menu toggles, and return focus when a modal-like menu closes. Test at desktop and mobile sizes.
Common mistake to avoid
Do not trap focus inside a simple dropdown unless it is intentionally a modal dialog. Support expected keyboard movement without surprising users.