Themes are written using Sass to keep things modular and reduce the need for repeated selectors across files. Make sure that you have the reveal.js development environment installed before proceeding: https://revealjs.com/installation/#full-setup
## Creating a Theme
To create your own theme, start by duplicating a ```.scss``` file in [/css/theme/source](https://github.com/hakimel/reveal.js/blob/master/css/theme/source). It will be automatically compiled from Sass to CSS (see the [gulpfile](https://github.com/hakimel/reveal.js/blob/master/gulpfile.js)) when you run `npm run build -- css-themes`.
Each theme file does four things in the following order:
1. **Include [/css/theme/template/mixins.scss](https://github.com/hakimel/reveal.js/blob/master/css/theme/template/mixins.scss)**
Shared utility functions.
2. **Include [/css/theme/template/settings.scss](https://github.com/hakimel/reveal.js/blob/master/css/theme/template/settings.scss)**
Declares a set of custom variables that the template file (step 4) expects. Can be overridden in step 3.
This is where you override the default theme. Either by specifying variables (see [settings.scss](https://github.com/hakimel/reveal.js/blob/master/css/theme/template/settings.scss) for reference) or by adding any selectors and styles you please.
4. **Include [/css/theme/template/theme.scss](https://github.com/hakimel/reveal.js/blob/master/css/theme/template/theme.scss)**
The template theme file which will generate final CSS output based on the currently defined variables.