Adwaita: Update switch styling

Use the new element names instead of the type name and style
classes.

Note that there is one problem with moving away from type names
here: it turns out that style properties only work if the selector
uses the type name.

gtk/theme/Adwaita/_common.scss

@@ -1955,14 +1955,15 @@ GtkSwitch {
   -GtkSwitch-slider-width: 45px; // 55px is the right value to make it as tall
                                  // as buttons, not doing that for now
   -GtkSwitch-slider-height: 27px;
+}
 
+switch {
   font-weight: bold;
   font-size: smaller;
   outline-offset: -4px;
   box-shadow: inset 0 1px transparentize(black, 0.9), // needs to be set here
               _widget_edge();                         // otherwise it gets
                                                       // clipped
-  &.trough {
   // similar to the .scale
   border: 1px solid $borders_color;
   border-radius: 3px;
@@ -1998,15 +1999,14 @@ GtkSwitch {
         background-image: linear-gradient(to bottom, $selected_bg_color);
         box-shadow: none;
       }
+  }
   &:insensitive {
         color: $backdrop_insensitive_color;
         border-color: $backdrop_borders_color;
         background-image: none;
         background-color: $insensitive_bg_color;
   }
-    }
-  }
-  &.slider {
+  & slider {
     border: 1px solid;
     border-radius: 3px;
     @include button(normal);
@@ -2047,7 +2047,6 @@ GtkSwitch {
       &.slider:active { border-color: $selected_borders_color; }
     }
   }
-
 }
 
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