Add Quantity Selector & Cart Button

I want every product on my site to show a small “- / +” quantity selector paired with a single Add-to-Cart button so shoppers can pick the exact number of items they need and drop them straight into the cart in one click.

Here is what I need from you:

• Build a lightweight, responsive quantity counter (stepper plus manual entry) that sits flush with my current product layout, on both desktop and mobile.
• Wire the Add-to-Cart action so it passes the chosen quantity to the cart using the store’s native API or endpoint—Ajax where possible to avoid page reloads.
• Keep styling consistent with my existing theme; no visual surprises.
• Supply clear installation steps (or perform the install directly if I give you access) and a brief test video or staging link so I can verify everything is working.

I’m flexible on exact tech choices; just choose something clean, well-commented, and easy to maintain. Let me know the approach, timeframe, and any access you’ll need and we can get started right away.