The QSS arrow styles only set width/height without specifying an image
or border-based triangle, so Qt fell back to platform-drawn arrows that
were invisible against the dark button background (#45475a).
Use CSS border triangles to render visible arrows in #cdd6f4 (Catppuccin
Mocha text color) with hover (#f5e0dc) and disabled (#6c7086) states
for spin boxes, combo boxes, and header sort indicators.
