Write an Accessibility Design Checklist

Create an accessibility design checklist for a [WEB APP / MOBILE APP / MARKETING SITE].

The checklist should cover design-phase accessibility decisions (not just development implementation). Target: WCAG 2.1 AA compliance.

Organise by category:

**Colour and contrast**
**Typography and readability**
**Interactive elements (buttons, links, forms)**
**Images and media**
**Navigation and focus management**
**Responsive and touch targets**
**Content structure and hierarchy**
**Error states and feedback**

For each item:
- Clear description of what to check
- Why it matters (brief)
- Pass/fail criteria
- Common mistake to avoid

End with a "quick wins" section — the 5 most common accessibility design failures to fix immediately.