Three fixes from the last round: (1) no border in any state — the resting button is just the glyph;
(2) the hover fill spans the full 22px height of the section header, not a short padded box;
(3) the fill is a neutral darken of the grey header — never a tint; the old near-white #f0f6ff
read as a bright white patch on the grey bar. Header bar is the real grey (#e5e7eb) with its inset top
highlight, so the fill is judged against the true background. Dial the fill + shape, then copy the readout into the plan.
Before — visible border, short padded box, near-white #f0f6ff hover (hover it).
After — no border, full-height tinted fill on hover only (hover it).