GTK theme has some inconsistencies
Maybe because Adwaita had some changes, but the last version of Darktable shows some rough edges in the UI, like
- When scrolling to the top or the bottom of an scrollview, an opaque overlay appears occluding some of the content
- In the settings window, there are 0 margin between the content and the GtkViewport
- The scrollbars don't have the "autohide" behavior all the Gnome apps have, they have little to none contrast with the background, and clicking on them doesn't change their color to reflect the change of state
- In the lightroom view, there are two "scrollbars" (they show your position, but if you click on them they toggle the left and right sidebars). But they use the background and foreground colors interchanged, so it's not clear what they do if you don't know it beforehand
And these are some of many UI issues. Maybe I could draft a PR to fix some of these if you want it, but I guess some discussion will be necessary before touching UI related stuff.
I attach some examples with quick-drawn annotations