WrapBootstrap - Wintertide Admin Theme | 1,00 MB
All of the views you see here (sign in, sign up, users, etc) are already split up so you don't have to waste your time doing it yourself! The layout.erb file includes the header, footer, and side navigation and all of the views are broken out into their own files.
If you aren't using Ruby, there is also a set of plain HTML files for each page, just like you would expect.
DEMO:
https://wrapbootstrap.com/theme/wintertide-admin-theme-WB0551736