High Contrast themes have "focusBorder" color that is the same for the active and unfocusedActive tabs, i.e. the active tabs in different groups:

:

Because of that it is somewhat harder to distinguish which group currently has the focus. It would be better if the border line of the active tab in unfocused group is dotted (to be different than the hovered tabs that have dashed border line). Or, even better, it would be nice if you add one new color setting available to themes, e.g. "unfocusBorder", or something like that.