Created attachment 254001 [details] Screenshot With GTK+ themes where the background of the scrollbar is set to transparent, the scrollbar painting does not seem to be blended with the web view as background, and the scrollbar marker is just painted over and over, without ever clearing the background. Reported downstream for the MosSky theme here: https://github.com/dasnoopy/moslight-themes/issues/14 The theme author commented: > it seems to be something related with webkitgtk and the new overlay scrollbars > introduced with gtk+ 3.16. As workaround I'll set a white background for > scrollbars. Probably there is something that should be done in the WebKitGTK+ side to have the transparent background in scrollbars render properly blended over the web content.