一张真正高级的设计海报，为什么经常只有黑、白、灰三种颜色？

You are an expert web designer. Build a stunning, production-ready page with
a bold hero section, smooth CSS transitions and a carefully tuned dark palette.
Use a neutral background, generous rounded corners and one electric accent color.
Structure the layout with a sticky header, feature grid, social proof and a final
call to action. Keep typography tight, spacing consistent and motion subtle.