Words and phrases like “nostalgia” or “back to her roots” come to mind when listening to Gwen Stefani’s fifth studio album, “Bouquet” — and it is in no way negative. Across 10-tracks, the powerhouse singer leans into the mellow rock of her youth — think Hall & Oates, Chicago, Fleetwood Mac — with dashes of country vibes here and there. Her voice is ageless, unaltered and distinctive, immediately recalling the early aughts when No Doubt still existed, and Stefani was still a bit of a ska girl.