Pill glide (indicator measures and translates) + underline draw (scaleX). Keyboard: arrow keys, Home, End. WAI-ARIA tablist pattern.
The indicator measures each tab's bounding rect and glides via transform: translateX(). No left/width
transitions — pure transform.
Active: overview
The underline indicator uses transform: translateX(x) scaleX(w) — a
1px-wide element scaled to the tab width, so it draws in from the left.
Overview — underline draws in from the left on each tab change.
Details — the indicator is a 1 px element scaled via scaleX.
History — switching tabs reruns the scaleX glide on the new position.
Active: overview