PayPay Style Design System (DESIGN.md, Japanese UI)

Design policy: The "approachability × call to action" of a fintech startup brand. Huge headings (hero H1 at 55px, Hero line-height 88px = ×1.6) + bold 700 weight create a strong, bright campaign feel. - Density: Generous whitespace, with line spacing of ×1.6–2.0 for a relaxed feel. CTAs stand out with PayPay Blue #3895FF rounded corners. - Keywords: Friendly, Bold Headlines, Vivid Blue + Red Accent, Campaign-driven