Picks the tab icon URL. In dark theme the icon is always the dark variant. In light theme it's
the near-black variant regardless of selection — every current host keeps the active tab's header
on a plain light background rather than a dark/tinted one (see
dock-layout-wrapper.simple-mode.scss's "SIMPLE-MODE TAB SELECTION LOOK" region), so a selected
tab needs the same contrast as an unselected one — a mid-slate fallback is used when the selected
state is unknown (undefined).
Picks the tab icon URL. In dark theme the icon is always the dark variant. In light theme it's the near-black variant regardless of selection — every current host keeps the active tab's header on a plain light background rather than a dark/tinted one (see
dock-layout-wrapper.simple-mode.scss's "SIMPLE-MODE TAB SELECTION LOOK" region), so a selected tab needs the same contrast as an unselected one — a mid-slate fallback is used when the selected state is unknown (undefined).