CSS navbar and color tweaks (#13609)

* CSS and color tweaks

- Unify navbar-style menus
- Fix admin bar overlapping menu bar
- Fixes file edit comment box
- Fix double border on review box
- Fix review timeline icons

* Many fixes to new-menu and navbar layout enhancements

* misc settings fixes

* navbar tweak

* fix pr tabs

* branch tag and arc color tweaks

web_src/less/_admin.less

@@ -44,11 +44,6 @@
     }
   }
 
-  .ui.header,
-  .ui.segment {
-    box-shadow: 0 1px 2px 0 var(--color-secondary);
-  }
-
   &.user {
     .email {
       max-width: 200px;