Features for my custom e-commerce website

My clothing-brand site is fully custom and runs on a straightforward HTML, CSS, and vanilla JavaScript stack. I’d now like to extend its functionality in two clear areas:

1. Product filtering by size and color
Visitors should be able to select one or multiple sizes and/or colors and instantly see only the matching items without a full page reload. I’m open to your preferred approach—query-string manipulation, AJAX calls to a JSON feed, or another lightweight solution—as long as the UX stays snappy on mobile and desktop.

2. Simple, browser-based inventory management
I’d like an admin-only panel (can be a protected route or a modal login) where I can update stock quantities and toggle “out of stock” status. A small CSV import/export option would be a bonus but isn’t mandatory.

Please include links to live sites or repos where you’ve implemented similar dynamic filtering or lightweight inventory tools—seeing real examples helps me gauge code quality and performance.

Deliverables (acceptance criteria)
• Clean, commented HTML/CSS/JS that drops into my existing codebase.
• Filtering UI that works across the latest Chrome, Firefox, Safari, and mobile browsers.
• Admin interface that lets me update inventory without touching code.
• Brief read-me outlining file locations and any setup steps.

I’m ready to start as soon as I find the right fit and can respond quickly to questions, so feel free to outline your approach and timeline along with those examples.