(In reply to Matthias Clasen from comment #0)
> Both the 'underflow' (the dotted lines) and the overflow in the scrolled
> window in the overview is a solid gray rectangle, instead of the subtle
> transparent overlay you get with Adwaita.

In the wizard? A screenshot would be even more helpful.

no, in the overview

Created attachment 302994 [details]
screencast

<Lapo_> zeenix: remove the "content-bg" class from BoxesCollectionView and kill the corresponding style from the app shipped css > FIXED
<Lapo_> zeenix: did I tell you that there's way too much stuff in the app shipped css, right? yes I did :-)
<Lapo_> zeenix: the content-bg class and style applied there does nothing but breaking the overshoot/undershoot
<Lapo_> zeenix: if you want that darkening the class mush be applied to the GdMainIconView

commit: 55a6c15b8eefb043077f23f4fb47b97c11942978

    ui: Drop redundant use of "content-bg" custom theme

    Don't overuse custom "content-bg". In case of main/collection view, use
    of this theme breaks the transparent theming of underflow and overflow
    indicators.