Html Tailwind Guideline: Colors — Use bg-linear-to-* for gradients. Description: Tailwind v4 uses bg-linear-to-* syntax for gradients. Do: bg-linear-to-r bg-linear-to-b. Don't: bg-gradient-to-* (deprecated in v4). Good Example: bg-linear-to-r from-blue-500 to-purple-500. Bad Example: bg-gradient-to-r from-blue-500 to-purple-500. Severity: Medium. Docs: https://tailwindcss.com/docs/background-image.