Fix: Background Image fix for dark theme loading change. (#8292)

## Summary

The variable whose name implied it was just an image URL bundled other
background pieces.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8292-Fix-Background-Image-fix-for-dark-theme-loading-change-2f26d73d36508177ae7bc24ae3cb027b)
by [Unito](https://www.unito.io)

manifest.json

@@ -11,5 +11,6 @@
     }
   ],
   "display": "standalone",
-  "theme_color": "#000000"
+  "background_color": "#172dd7",
+  "theme_color": "#f0ff41"
 }