Simple Responsive Website Build

I need a lightweight, fully responsive website coded only with vanilla HTML, CSS and JavaScript—no external frameworks, libraries or CMS. The goal is to give me clean, well-commented files that I can later expand with my own content.

What I expect
• A mobile-first layout that fluidly adapts from small phones to large desktops, tested across the latest versions of Chrome, Safari and Firefox.
• Standard sections such as a hero/banner, navigation bar, main content area and footer (feel free to use placeholder text and images for now).
• Smooth, unobtrusive JavaScript where necessary—for example, a collapsing menu, simple form validation or a back-to-top button.
• All code neatly organised in clear folders (e.g., /css, /js, /images) with a short README explaining how to tweak colours, fonts and copy.

Acceptance criteria
1. Pages pass Google’s Mobile-Friendly Test.
2. Desktop Lighthouse performance score of 90+.
3. Delivered as a single zipped package that I can unzip and open offline without setup.

Once you have a working demo online (GitHub Pages is fine), send the link so I can review. After approval, hand over the source files and README.