Theming done

openspec/changes/archive/2026-02-11-dch-theming/proposal.md

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+## Why
+
+Add modern theming controls (dark/light/high-contrast) to improve accessibility and give the site a polished, customizable "WOW" experience.
+
+## What Changes
+
+- Add three user-selectable themes: **Dark**, **Light**, and **High Contrast**.
+- Add a floating theme switcher "notch" on the right edge of the screen:
+  - positioned just below the primary nav bar
+  - leaves enough vertical space for secondary navigation
+  - hover state includes a tasteful animation
+- Theme switching uses a smooth transition (not an abrupt flash).
+
+## Capabilities
+
+### New Capabilities
+- `site-theming`: Theme tokens and a theme application mechanism that can switch between Dark/Light/High Contrast across the site.
+- `theme-switcher-notch`: A floating, accessible UI control (right-side notch) that lets the user switch themes.
+
+### Modified Capabilities
+- `wcag-responsive-ui`: Extend accessibility baseline to include theme switching requirements (keyboard, focus, reduced motion) and ensure High Contrast theme is supported.
+
+## Impact
+
+- Affected UI/CSS: global design tokens (CSS variables), background layers, card/CTA styling, focus styling.
+- Affected layout: a new floating notch component that must not overlap navigation across breakpoints.
+- Affected UX/accessibility: keyboard navigation and motion preferences during theme transitions.