The secondary/glass Button variant used a flat, fairly opaque black or
white tint with no blur, so it didn't read as glass and clashed with
the hue-shifting hero background. Add a backdrop blur and a hairline
border (matching the app's existing glass-bar/glass-panel treatment)
and lower the tint opacity.
Wire up the already-computed but unused --mf-accent-muted token as
--color-accent-muted, and use it for the accent Button variant's text
instead of the higher-chroma --color-accent-soft, so it reads softer.