spotlight on ctrl+space, theme browser on ctrl+shift+up/down, no backdrop behind the theme list

src/apps/officer-web/locales/en-GB.json

@@ -478,11 +478,11 @@
     "codeEditor": "Code Editor"
   },
   "theme": {
-    "pillTitle": "Theme: {{name}}  ·  ctrl+shift+←/→ cycle · ctrl+shift+space browse · ctrl+shift+f {{starAction}}",
+    "pillTitle": "Theme: {{name}}  ·  ctrl+shift+←/→ cycle · ctrl+shift+↑/↓ browse · ctrl+shift+f {{starAction}}",
     "pillLabel": "Theme: {{name}}",
     "star": "star",
     "unstar": "unstar",
-    "cycleHint": "ctrl+shift+←/→ cycle · ctrl+shift+space browse",
+    "cycleHint": "ctrl+shift+←/→ cycle · ctrl+shift+↑/↓ browse",
     "everyShortcutHint": "ctrl+? for every shortcut",
     "favouritesOnly": "Favourites only ({{count}})",
     "favourites": "Favourites ({{count}})",