## Bug
Three component stylesheets (`app.scss`, `sidebar.scss`, `theme-switcher.scss`) carried `:where(.dark) &` rules to react to the `<html>.dark` class — the same pattern Tailwind uses internally. **Angular's emulated CSS encapsulation descends into `:where()` and rewrites its contents with the `_ngcontent-XXX` scoping attribute**, so the produced selector looked like:
```css
:where(.dark[_ngcontent-c0]) .shell-main[_ngcontent-c0] { ... }
```
`<html>` carries `.dark` but no `_ngcontent` attribute — the rule never matched.
Visible symptom: the main page background stayed light even when `.dark` was on `<html>` and every Tailwind `dark:` utility in the templates was working correctly. Sidebar hover/focus/active states and the theme-switcher menu surface had the same bug.
## Fix
- **`app.scss` and `sidebar.scss`** switch to `:host-context(.dark)`. The Angular compiler recognises this directive and expands it without forcing the ancestor (`<html>`) to carry the scoping attribute. Compiled output:
```css
.dark[_nghost-c0] .shell-main[_ngcontent-c0],
.dark [_nghost-c0] .shell-main[_ngcontent-c0] { ... }
```
The second selector matches `<html>.dark` as an ancestor of `<app-root>` (the host) — exactly what we want.
- **`theme-switcher` switches to `ViewEncapsulation.None`**. Its CDK menu opens in an overlay portal appended to `<body>` — outside the component's host subtree — so even `:host-context()` would miss it. With encapsulation disabled, the styles emit globally; the BEM-style class names (`.theme-switcher__menu`, `.theme-switcher__item`, ...) keep the rules contained without leaking.
## Drive-by
- Remove the right border on the `.header__logo-zone`. The visible hairline above the sidebar was extra noise — the alignment of widths already carries the visual relationship to the rail below.
## Why not also rip out the `dark:` Tailwind utilities used in the templates?
They work. They're emitted into the global Tailwind sheet, sit outside view encapsulation, and already handle the `.dark` ancestor lookup via their own selector (`:where(.dark, .dark *)`). The bug was specifically about component-authored CSS *inside* an SCSS file under emulated encapsulation.
## Test plan
- [x] `pnpm exec nx run-many -t lint test build --projects=portal-shell` — green (33 / 33 specs).
- [x] Inspect the produced CSS: `:host-context(.dark)` expands to both `.dark[_nghost-XXX]` and `.dark [_nghost-XXX]` selectors, no `_ngcontent` attribute leaked into the `.dark` portion.
- [ ] Manual: pick dark mode → `/` shows the dark page background; sidebar hover / active / focus visibly switches; theme-switcher menu opens with the dark surface.
- [ ] Manual: header no longer shows a vertical hairline between the logo zone and the search/actions cluster.
---------
Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #87
julien
3a0a9c700d