Focus ring
The visible indicator a user agent draws around the currently focused element, announcing keyboard or programmatic focus position. The ring is the only cue keyboard users have for tracking focus.
Each engine ships a default focus ring; authors may replace it
with a custom outline or box-shadow, but must not remove it
without a visible substitute. The :focus-visible pseudo-class
matches keyboard focus and excludes mouse-click focus on
buttons, letting designs hide the ring on click while keeping it
for Tab. The ring must meet a 3:1 contrast ratio against adjacent
colours per WCAG 1.4.11.