> For the complete documentation index, see [llms.txt](https://harmonycms.gitbook.io/platform/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://harmonycms.gitbook.io/platform/marketplace/theme.md).

# Theme

## Overview

A theme is a collection of files (.twig, .css, .js, ...) that determine how the CMS website looks.\
The goal of a theme system is to let the end user change the look of the entire site all at once, on every page, while leaving the content intact. Even if the site has thousands of pages, you can change to a new theme quickly.