docs: add backlog items 999.20 (dark mode/theming) + 999.21 (styling refresh)

.planning/ROADMAP.md

@@ -654,6 +654,32 @@ Plans:
 
 - [ ] TBD (promote with /gsd-review-backlog when ready)
 
+### Phase 999.20: PWA dark mode / theming — ship a full dark theme + light/dark/system switch (BACKLOG)
+
+**Goal:** [Captured for future planning] Ship a complete dark theme for the PWA plus a light/dark/system theme switch. **Phase 17 lays the token-architecture groundwork** — it restructures `apps/pwa/src/styles/tokens.css` from a single light `:root` into a themeable semantic-token layer that can be swapped via `data-theme` / `prefers-color-scheme`, with light staying the default and only-shipped theme. This backlog item is the follow-through that consumes that seam: author the actual dark palette values (including the Schedule-X `--sx-color-*` calendar overrides at the bottom of tokens.css), wire `prefers-color-scheme`, add a persisted in-app toggle in the /admin or Settings surface (light / dark / system), and verify both themes render cleanly across every route (calendar, lists, admin, settings sheet, login) via `playwright-cli` + the Phase 7 `layout.spec` profiles.
+
+**Context:** Deferred out of Phase 17 (2026-06-17) during `/gsd-discuss-phase 17` to keep that phase scoped to phone-layout polish + branding assets. Phase 17's token restructure is the explicit enabling groundwork, so this should be cheap to pick up afterward. Related: Phase 17 (UI Optimization & Polish — the groundwork), 999.21 (modern styling refresh). Tags: pwa, theming, dark-mode, tokens, accessibility, settings, prefers-color-scheme.
+
+**Requirements:** TBD
+**Plans:** 0 plans
+
+Plans:
+
+- [ ] TBD (promote with /gsd-review-backlog when ready)
+
+### Phase 999.21: PWA modern visual styling refresh — contemporary look across the app (BACKLOG)
+
+**Goal:** [Captured for future planning] A broader "more modern, visually appealing" styling pass across the PWA — beyond the bounded in-system polish of Phase 17. Candidate scope: a contemporary refresh of high-visibility surfaces (login, calendar shell, event form, lists, admin), revisiting elevation/shadows, radii, spacing rhythm, typography scale, and control states, potentially reworking specific component layouts. Explicitly **flagged for a future milestone**, not v1.1 — it is a visual-overhaul track with real redesign risk and should be scoped/sequenced on its own rather than bolted onto a polish phase. Best sequenced after the Phase 17 token groundwork and 999.20 (dark mode) so the refresh is theme-aware from the start.
+
+**Context:** Deferred out of Phase 17 (2026-06-17) during `/gsd-discuss-phase 17`. The user scoped Phase 17 to layout polish + branding (logo/favicon/icon assets) + theme-token groundwork, and routed the open-ended styling refresh here for a future milestone to avoid an unbounded redesign inside a polish phase. Related: Phase 17 (the polish baseline), 999.20 (dark mode / theming). Tags: pwa, ui, styling, redesign, design-system, future-milestone.
+
+**Requirements:** TBD
+**Plans:** 0 plans
+
+Plans:
+
+- [ ] TBD (promote with /gsd-review-backlog when ready)
+
 ### Phase 18: Auto timezone detection and ability to change timezone
 
 **Goal:** Make the household timezone an explicit, stored, user-changeable setting — auto-detected from the browser at first run, changeable from the role-gated /admin Settings — and route the server-side all-day "9 AM local" reminder computation through it (replacing the implicit `process.env.TZ` fallback), without touching the already-correct browser-local display/timed-write path.