Settings
Primitive: a popover="auto" panel in the top layer. The browser supplies light dismiss, Escape and the toggle events; the script drives the invoker (a native popovertarget would toggle the panel closed on the click that follows a hover-open), adds hover-to-expand (mouse only; a click pins a hover-opened panel), placement where anchor positioning is absent, the fallback path where popovers are unsupported, preview on hover, persistence and the theme-colour sync.
Options: label, schemeControl (full | tint-only), tints, schemes, resetOnReselect, hoverOpen, id, attributes.
Keyboard and focus: Enter/Space on the gear toggles; Escape closes; focus returns to where it was when the panel opened (the gear after a click open; unchanged after a hover open); Tab enters the panel; arrow keys move within each radio group; the panel never hover-closes while any control inside has focus.
Baseline: Popover and @starting-style are newly available and used behind a capability attribute; anchor positioning and corner-shape are limited and only enhance.