How users control themes — one global selector with optional per-surface overrides
| Setting | Stored as | Effect |
| Color mode | theme_mode: "dark" | "light" | Switches all color tokens |
| Glass style | theme_glass: "true" | "false" | Adds .theme-glass class → blur, rgba surfaces, iOS accents, pill shapes |
| Serif headings | theme_serif: "true" | "false" | Adds .theme-serif class → Fraunces for headings |
| Per-surface override | theme_blog_mode, theme_dashboard_mode | Override color mode for one surface only |