Appearance contains settings that apply beyond a single document. The controls for an individual page, its paper, background, width and zoom, are on the writing surface itself and are covered on the Editor page.
Color overrides
The accent colors used through the interface can be overridden. A book may also be given its own accent, which is applied whenever that book is open, so two books can be told apart at a glance.
Custom draft stages
The stages shown on Binder rows, Outline, Draft, Revision and Final Copy by default, are editable. Define the set that matches how you actually work, and the palette applies wherever a stage is displayed.
Footnote style
Footnote presentation is set per book, so a nonfiction project and a novel in the same account can differ.
The paper bar
The bar with the paper and background controls can be set to hide itself when not in use, which removes a line of interface from the writing surface without removing access to the controls.
Where these settings live
Interface preferences are stored on the device on which they are set, not on the server, so they do not follow you between machines. This is stated in clause 4.5 of the Privacy Policy.