With no art, the sidebar's art widget moves out of the playlist list's
frame onto the window below it, so the panel is set into the gray like the
visualizer rather than into a white box. A tall debossed panel is now
shaded along its top and bottom exactly as the 62 px visualizer is, flat
in the visualizer's color between, instead of one gradient stretched over
its whole height, which read as gray. The scrollbar thumb is shaded the
same way, like a button.
The sidebar's art square, when a track has no art, is now the list's own
background with a rounded panel set into it, debossed like the visualizer
and the now-playing panel. paint_deboss takes its rims in pixels when
asked, so a panel as tall as the sidebar is recessed as much as a short
one rather than fading over 16 px.
The app style now paints the scrollbars itself: the trough runs the full
length with no arrow buttons, and the thumb gets the buttons' 4 px corners
and emboss, with rims as tall in pixels as a button's however long the
thumb. Bar thickness moved from QSS to the style's pixel metric, since any
QSS rule on a scrollbar part makes Qt draw the whole bar, arrows included.
trav