Stylelint is a css linter: https://stylelint.io/
As part of this change we have added two javascript scripts:
```
pnpm lint:css
pnpm lint:css:fix
```
Look at `.vscode/settings.json.sample` and `.vscode/extensions.json` for
configuration in VSCode.
---------
Co-authored-by: Joffrey JAFFEUX <j.jaffeux@gmail.com>
A first step to adding automatic dark mode color scheme switching. Adds a new SCSS file at `color_definitions.scss` that serves to output all SCSS color variables as CSS custom properties. And replaces all SCSS color variables with the new CSS custom properties throughout the stylesheets.
This is an alpha feature at this point, can only be enabled via console using the `default_dark_mode_color_scheme_id` site setting.
