chore(styles): adopt bg color for dock background

Replace transparent background with theme variable and tidy up CSS.

- New Features
- Enhancements
    - Use `@bg` instead of `alpha(#fff, 0.07)`
    - Remove unused comment blocks
- Bug Fixes
    - Clean up duplicated CSS comments and whitespace

styles/dock.css

@@ -1,5 +1,5 @@
 #dock {
-    background-color: alpha(#fff, 0.07);
+    background-color: @bg;
     padding: 4px 4px;
     margin: 4px 4px;
     border: none;
@@ -96,4 +96,4 @@
 /*   min-height: 0px; */
 /*   margin-top: 0px; */
 /*   background-color: transparent; */
-/* } */
+/* } */