What are the WCAG 2.1 contrast ratio requirements and how do you check them in Salesforce designs?

WCAG 2.1 defines two levels of contrast compliance:

1. AA (minimum): Normal text (below 18pt/14pt bold) requires a contrast ratio of at least 4.5:1 against its background. Large text (18pt+ or 14pt+ bold) requires 3:1. UI components and graphical objects (icons, chart lines, input borders) also require 3:1.
2. AAA (enhanced): Normal text requires 7:1; large text requires 4.5:1. In Salesforce design: check contrast using tools like the Stark Figma plugin, WebAIM Contrast Checker, or browser DevTools accessibility panel. SLDS tokens are pre-checked for AA compliance on white backgrounds, but custom themes created in Lightning Theme Builder must be manually audited — especially brand colours used on coloured hero banners. Dark mode combinations require separate testing. Always test with real content, not placeholder text, as short labels on coloured badges are common failure points.