Created attachment 151491 [details]
Current behavior followed by expected behavior followed by Qt equivalent (KDE system settings)

SUMMARY
When you hover over an item of a GTK list (for example a GtkListBox or a GtkStackSidebar) the background color of such item becomes #3daee9 (in the default breeze dark), which is the same color as the selected items in the list. These colors should actually be different.

STEPS TO REPRODUCE
1. Open an application that contains a list (e.g. the sidebar on the GTK file picker), or quickly create a layout in Glade
2. Select an item in the list
3. Hover over a different item

OBSERVED RESULT
The two items have identical background colors (#3daee9 in the default breeze dark).

EXPECTED RESULT
The selected item has the correct color, however the hovered one should be different (e.g. #1f485e on the default breeze dark).

SOFTWARE/OS VERSIONS
GTK Version: 3; might also happen on 2 and 4 but I can't test them
OS: Arch Linux
KDE Plasma Version: 5.25.4
KDE Frameworks Version: 5.97.0
Qt Version: 5.15.5

ADDITIONAL INFORMATION
I managed to fix it for Breeze Dark by modifying gtk.css in the "Lists" section:

sed -i '2336s/theme_selected_bg_color_breeze/theme_unfocused_selected_bg_color_breeze/' gtk.css