Design issue capturing the request to let users customize document-artifact
colors and switch between theme variants, instead of everyone getting one
forced theme. Notes the two separable pieces (structure/skin split via CSS
variables as a prerequisite — the themes currently hardcode colors — and a
switching mechanism), the preset-vs-raw-CSS security tradeoff, dark-mode
interaction, and deck as the concrete trigger. References the existing
planning docs on theme variants/palettes.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
