Currently, it seems that the scrollbar is following Adawaita-light rather than Adwaita-dark.
Epiphany version : 3.36.0-27-g2a31b3fdc
WebKitGTK version : 2.28.0
This is on purpose, we now always use the light variant to render form controls and scrollbars. See bug #197947
Hm, would it be possible to have the window's scrollbar only follow the stylesheet (unless CSS modifies it obviously) while keeping the rest stylesheet-independent as per the plan?
Nope, switching GTK theme in the same process is not realistic.
I guess this is WONTFIX, then? At least for 2.28?
Maybe we could do the right thing in trunk somehow? But we have a hardcoded light scrollbar there currently....