You are not looking at the GetSimple Seascape Theme itself. This html file is a brief introduction to the Skeleton responsive grid and boilerplate css on which the Seascape theme is built. It is left in the theme folder as a starting point for users who want to edit the theme.
Skeleton is a small collection of well-organized CSS files that can help you rapidly develop sites that look beautiful at any size, be it a 17" laptop screen or an iPhone. It's based on a responsive grid, but also provides very basic CSS for typography, buttons, forms and media queries. Go ahead, resize this super basic page to see the grid in action.
Skeleton is built on three core principles:
The easiest way to really get started with Skeleton is to check out the full docs and info at www.getskeleton.com.. Skeleton is also open-source and has a project on git, so check that out if you want to report bugs or create a pull request. If you have any questions, thoughts, concerns or feedback, please don't hesitate to email me at hi@getskeleton.com.