themes: Make disabled Expander arrow look disabled

If GtkExpander:sensitive was FALSE, the arrow still got the normal fg
colour, which made it look clickable, in contrast to the adjacent label.
Fix this by adding selectors to catch the applicable :disabled states.

Note: Needing these may indicate an oops in generic styles elsewhere,
but I couldn’t see any, so let’s just get it looking right for now.

Close https://gitlab.gnome.org/GNOME/gtk/issues/146

gtk/theme/Adwaita/_common.scss

@@ -3645,9 +3645,11 @@ expander {
     min-width: 16px;
     min-height: 16px;
     -gtk-icon-source: -gtk-icontheme('pan-end-symbolic');
-
     &:dir(rtl) { -gtk-icon-source: -gtk-icontheme('pan-end-symbolic-rtl'); }
 
+    &:disabled { color: $insensitive_fg_color; }
+    &:disabled:backdrop { color: $backdrop_insensitive_color; }
+
     &:checked { -gtk-icon-source: -gtk-icontheme('pan-down-symbolic'); }
   }
 

gtk/theme/Adwaita/gtk-contained-dark.css

@@ -1596,6 +1596,10 @@ expander title > arrow { min-width: 16px; min-height: 16px; -gtk-icon-source: -g
 
 expander title > arrow:dir(rtl) { -gtk-icon-source: -gtk-icontheme("pan-end-symbolic-rtl"); }
 
+expander title > arrow:disabled { color: #919494; }
+
+expander title > arrow:disabled:backdrop { color: #566164; }
+
 expander title > arrow:checked { -gtk-icon-source: -gtk-icontheme("pan-down-symbolic"); }
 
 expander title:hover > arrow { color: white; }

gtk/theme/Adwaita/gtk-contained.css

@@ -1616,6 +1616,10 @@ expander title > arrow { min-width: 16px; min-height: 16px; -gtk-icon-source: -g
 
 expander title > arrow:dir(rtl) { -gtk-icon-source: -gtk-icontheme("pan-end-symbolic-rtl"); }
 
+expander title > arrow:disabled { color: #8b8e8f; }
+
+expander title > arrow:disabled:backdrop { color: #c3c3c0; }
+
 expander title > arrow:checked { -gtk-icon-source: -gtk-icontheme("pan-down-symbolic"); }
 
 expander title:hover > arrow { color: #748489; }

gtk/theme/HighContrast/_common.scss

@@ -2769,6 +2769,9 @@ expander {
     min-height: 16px;
     -gtk-icon-source: -gtk-icontheme('pan-end-symbolic');
     &:dir(rtl) { -gtk-icon-source: -gtk-icontheme('pan-end-symbolic-rtl'); }
+
+    &:disabled { color: $insensitive_fg_color; }
+
     &:checked { -gtk-icon-source: -gtk-icontheme('pan-down-symbolic'); }
   }
 

gtk/theme/HighContrast/gtk-contained-inverse.css

@@ -1244,6 +1244,8 @@ expander title > arrow { min-width: 16px; min-height: 16px; -gtk-icon-source: -g
 
 expander title > arrow:dir(rtl) { -gtk-icon-source: -gtk-icontheme("pan-end-symbolic-rtl"); }
 
+expander title > arrow:disabled { color: gray; }
+
 expander title > arrow:checked { -gtk-icon-source: -gtk-icontheme("pan-down-symbolic"); }
 
 expander title:hover > arrow { color: white; }

gtk/theme/HighContrast/gtk-contained.css

@@ -1250,6 +1250,8 @@ expander title > arrow { min-width: 16px; min-height: 16px; -gtk-icon-source: -g
 
 expander title > arrow:dir(rtl) { -gtk-icon-source: -gtk-icontheme("pan-end-symbolic-rtl"); }
 
+expander title > arrow:disabled { color: gray; }
+
 expander title > arrow:checked { -gtk-icon-source: -gtk-icontheme("pan-down-symbolic"); }
 
 expander title:hover > arrow { color: #4d4d4d; }