**Steps to replicate the issue** (include links if applicable):
* Go to https://doc.wikimedia.org/codex/v2.0.0-rc.1/design-tokens/color.html
* Use the reading settings icon at the top right of the page to toggle between light and dark mode
**What happens?**:
* Toggling to dark mode should show dark mode variant of token values and previews
**What should have happened instead?**:
* All token values and previews stay in their light mode variants
Thank you @LucasWerkmeister for raising this in T383606#10788738.
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This is happening because we're relying on a property returned by VitePress's `useData` composable, `isDark`, which worked when we were using VitePress's color mode switcher. Now that we've using our own system where the color mode is stored in `sessionStorage`, we should update the colors page to use that data.
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### Acceptance criteria
- [] Switching color mode also switches the color swatches and values on the Colors tokens page