SEKISUI HOUSE Style Design System (DESIGN.md, Japanese UI)

Design policy: A serene, refined housing brand presence that uses an almost monochrome, restrained color palette with dark charcoal #3b3b41 as the sole accent. It has no flashy brand color, expressing dignity through typography and whitespace. - Density: Body text line-height is 1.6, headings are tight at 1.3. Generous whitespace and section division let the content breathe. - Keywords: Serene, refined, monochrome, Yu Gothic Pr6N, dignity of a housing brand - Characteristics: - Adopts TypeSquare (Morisawa) hosted Yu Gothic Pr6N (Medium / Bold) for Japanese text. It is a Pr6N variant distinct f