theme: Move basic selectors into _base.scss

.shell-link, .lowres-icon and .icon-dropshadow could be used globally.

For the icon shadow classes, they're used by officially supported
extensions.[1]

[1] https://gitlab.gnome.org/GNOME/gnome-shell-extensions/issues/168

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/938

data/theme/gnome-shell-sass/_widgets.scss

@@ -7,6 +7,7 @@
 /* WIDGETS */
 
 // Primary widgets
+@import 'widgets/base';
 @import 'widgets/entries';
 @import 'widgets/buttons';
 @import 'widgets/check-box';

data/theme/gnome-shell-sass/widgets/_app-grid.scss

@@ -20,16 +20,6 @@ $app_icon_padding: 24px;
 
 $app_grid_fg_color: #fff;
 
-// Outline for low res icons
-.lowres-icon {
-  icon-shadow: 0 1px 2px rgba(0,0,0,0.3);
-}
-
-// Dropshadow for large icons
-.icon-dropshadow {
-  icon-shadow: 0 1px 2px rgba(0,0,0,0.4);
-}
-
 // Icon tiles in the app grid
 .app-well-app,
 %app-well-app {

data/theme/gnome-shell-sass/widgets/_base.scss

@@ -0,0 +1,18 @@
+// Links
+.shell-link {
+  color: $link_color;
+
+  &:hover {
+    color: lighten($link_color, 10%);
+  }
+}
+
+// Outline for low res icons
+.lowres-icon {
+  icon-shadow: 0 1px 2px rgba(black, 0.3);
+}
+
+// Dropshadow for large icons
+.icon-dropshadow {
+  icon-shadow: 0 1px 2px rgba(black, 0.4);
+}

data/theme/gnome-shell-sass/widgets/_misc.scss

@@ -1,9 +1,4 @@
-// Links/URLs
-.shell-link {
-  color: $link_color;
-  &:hover { color: lighten($link_color,10%); }
-}
-
+// URLs
 .url-highlighter { link-color: $link_color; }
 
 // Rubberband for select-area screenshots

data/theme/meson.build

@@ -8,6 +8,7 @@ theme_sources = files([
   'gnome-shell-sass/_widgets.scss',
   'gnome-shell-sass/widgets/_app-grid.scss',
   'gnome-shell-sass/widgets/_app-switcher.scss',
+  'gnome-shell-sass/widgets/_base.scss',
   'gnome-shell-sass/widgets/_buttons.scss',
   'gnome-shell-sass/widgets/_calendar.scss',
   'gnome-shell-sass/widgets/_check-box.scss',