theme: Clean up some start menu styling

Use the same hover colors as used in other menus. Add some spacing between
the apps and categories columns. Add some spacing and padding in the
favorites bar

data/theme/cinnamon-sass/widgets/_startmenu.scss

@@ -20,26 +20,30 @@ $menu_outer_border_radius: $base_border_radius * 1.25;
   }
 
   &-favorites-button {
-    padding: $base_padding;
+    padding: $base_padding * 1.5;
     border-radius: $base_border_radius;
 
     &:hover { background-color: $lightest_bg_color; }
   }
 
-  &-categories-box { padding: $menu_outer_padding; }
+  &-categories-box { padding: $menu_outer_padding $base_padding * 2; }
   &-applications-box { padding: $menu_outer_padding; }
+  &-applications-inner-box {
+    &:ltr { padding-left: $base_padding * 2; }
+    &:rtl { padding-right: $base_padding * 2; }
+  }
 
   &-application-button {
     @extend %start_menu_button;
 
-    &-label { padding: 0 }
+    &-label { padding: 0; }
 
     &:highlighted { font-weight: bold; }
 
     &-selected {
       @extend %start_menu_button;
 
-      background-color: $lighter_bg_color;
+      background-color: $light_bg_color;
 
       &:highlighted { font-weight: bold; }
     }
@@ -48,14 +52,14 @@ $menu_outer_border_radius: $base_border_radius * 1.25;
   &-category-button {
     @extend %start_menu_button;
 
-    &-label { padding: 0 }
+    &-label { padding: 0; }
 
     &:hover { background-color: $lighter_bg_color; }
 
     &-selected {
       @extend %start_menu_button;
 
-      background-color: $lighter_bg_color;
+      background-color: $light_bg_color;
     }
 
     &-greyed {