exlab_wizard.ui.design

Design tokens. Mirrors DESIGN.md verbatim with the Frontend Spec §2.1 typography override (IBM Plex Sans body / system mono).

This module is the single Python source of truth for runtime design tokens. Per Frontend Spec §2.1.1, every UI module imports tokens from here rather than hard-coding hex / px / rem literals. The :root { ... } CSS block injected by ui/theme.py is generated from these constants so component CSS can use the canonical var(--color-*) names documented in DESIGN.md §07.

Update discipline: keep design.py and DESIGN.md in lock-step (see tests/unit/ui/test_design.py).