Joplin UI: Snippet headers & Account Settings

"As a city author, I need the authoring experience to have a logical visual hierarchy so that I am better able to understand the **Snippet headers & Account Settings** interface." - A City Author

This is a broken out section of the Joplin UI re-design.

#### Acceptance Criteria
- [ ] Matches styles from XD Design 👇
- https://xd.adobe.com/view/c533a077-9314-46a6-5db4-d4a7f8601e8f-b302/screen/ddcfa854-6b47-40ec-9f2b-72eb7bbc5916/Joplin-3-Phase-1-enhancements-Maps
- [ ] Matches CSS for Themes and Colors from Google doc 👇 "Phase 1 acceptance criteria"
- See Snippit Headers section: https://docs.google.com/document/d/1SdAro51Ppdi3Hirn1XkVviJ6nu89dDXtvvFKIX4T8t8/edit#heading=h.hcx9qfuiyue
- Also, Account settings section: https://docs.google.com/document/d/1SdAro51Ppdi3Hirn1XkVviJ6nu89dDXtvvFKIX4T8t8/edit#heading=h.xhjizopxtvs7

#### Technical Acceptance Criteria
- [ ] Matches any new structural patterns implemented into the new Joplin UI
- [ ] Checks for and removes any dead-css no longer being used.

Start with the linked XD design and the Google document's Snippet Headers and Account settings sections, then locate those interface areas in the Joplin UI. Done means the UI matches the specified visual hierarchy, themes, colors, and structural patterns, with unused CSS removed.

Written by the indexing model from the issue text.