Summary
- Write or change styles in `core/scss/` — the framework itself.
- Use whenever a component needs a new class, modifier, size or colour variant, when a Sass or CSS custom property is added or renamed, when dark mode or RTL behaviour is involved, and before touching `_variables.scss`, `_props.scss` or anything under `core/scss/ui/`.
- Covers where a style goes, the custom-property pattern and its build-time `--tblr-` prefix, dark mode, RTL, the docs markers, the SCSS unit tests and the lint/size gates.