Claws-Mail font color of selected items is incorrect with GTK-3.0

[mbenkmann]

Claws-Mail has a custom Gtk widget called GtkSCTree which it uses in at least the folder and summary view. This custom widget does not implement any CSS classes. When using the GTK-3.0 version of Claws-Mail+Yaru, for some reason of the .gtkstyle-fallback:selected{} rules found here

yaru/gtk/src/default/gtk-3.0/_common.scss

Line 104 in ca65553

background-color: $selected_bg_color;

only the background-color rule affects the selected entries in this custom widget. This causes a regression compared to the GTK-2.0 version of Claws-Mail+Yaru and makes the entries harder to read. The font color of a selected entry does not change to white as it should, but stays black and depending on the variant of Yaru being used this is more or less terrible to read. E.g. in the default version it results in black on red which is really painful.

The only way I found to fix this is to add a blanket catchall:

*:selected { color: $selected_fg_color; }