Shadcn Guideline: Customization — Extend variants with cva. Description: Add new variants using class-variance-authority. Do: Extend buttonVariants for new styles. Don't: Inline classes for variants. Good Example: variants: { size: { xl: "h-14 px-8" } }. Bad Example: className="h-14 px-8". Severity: Medium. Docs: https://ui.shadcn.com/docs/components/button.