Responsive HTML/CSS Webpage Build -- 2

I need a single-page site crafted with pure HTML5 and CSS3, mobile-first and fully responsive. The layout is straightforward: header, navigation bar, main section, and footer. Inside the main section, include a contact form with the fields Name, Email, and Message, wired to a dummy action for now.

The aesthetic is minimalist and leans on a neutral palette—ample white space, subtle greys, clean typography. Code quality is paramount: use semantic tags, well-organized external stylesheets, clear class naming, and helpful comments. No inline styles or heavyweight frameworks, just clean, well-structured code. Media queries should cover common breakpoints so the page looks polished on phones, tablets, and desktops.

Deliverables
• index.html and styles.css, both W3C-valid
• A brief README outlining font choices and breakpoints
• Any placeholder assets used

I’ll review in Chrome, Firefox, and Safari at 375 px, 768 px, and full width. If anything breaks at those sizes, I’ll request adjustments. Let me know your timeframe and any clarifications you need.