Mint-Y GTK4: text selection is invisible in spin buttons (wrong CSS selector)

Hi there,

mint-themes 2.3.8, Linux Mint 22.3, GTK 4.

Selecting text inside a GtkSpinButton shows no selection highlight. The text stays on the plain background, while the same gesture in a GtkEntry next to it is highlighted normally. Reproducible in any GTK4 app; gtk4-widget-factory
(package gtk-4-examples) is enough.

The generated sheet has, at /usr/share/themes/Mint-Y/gtk-4.0/gtk.css lines 3037,
3044 and 3051 (same in the -Sand/-dark variants, gtk-dark.css lines 3034/3041/3048):

entry > text > selection, spinbutton text > text > selection, … {
  background-color: #c5a07c; }

spinbutton text > text > selection is one text too many for a horizontal spin button, whose node tree is spinbutton > text > selection, so the selector matches nothing.

It looks like the SCSS appends > text > selection to a variable that already expands to "entry, spinbutton text".

GTK4's own default theme handles both shapes:

spinbutton.vertical > text > text > selection,
spinbutton:not(.vertical) > text > selection,
entry > text > selection { … }

(from /org/gtk/libgtk/theme/Default/Default-light.css, extracted with gresource extract /usr/lib/x86_64-linux-gnu/libgtk-4.so.1 …)

Adding the spinbutton:not(.vertical) > text > selection branch to the three rules (normal, color:, and :disabled) fixes it. Application-side workaround,

For reference:

spinbutton > text > selection {
  background-color: @theme_selected_bg_color;
  color: @theme_selected_fg_color;
}

The content of the bug report was generated by AI, but I checked it and it seems correct to me.
I haven't checked whether this issue is present in other themes.

Have a great day.

Start with the SCSS that generates the selection rules appearing in gtk-4.0/gtk.css around lines 3037, 3044, and 3051, plus the corresponding gtk-dark.css and -Sand/-dark variants. Check the selector against gtk4-widget-factory, update the three normal, colored, and disabled rules, and verify that horizontal spin-button text selection is visible.