How to Enable Sticky Add to Cart in Shopify Dawn Theme

Dawn's product page behaves differently by screen size, and there's no single "sticky cart" toggle that covers both.

Steps

On desktop, Dawn's two-column product layout already keeps the buy box visible alongside the image as shoppers scroll — this is the default grid layout, not an optional setting.
On mobile, the layout stacks vertically and the add-to-cart button scrolls away with the rest of the page — Dawn doesn't include a persistent bottom bar out of the box.
If a sticky mobile add-to-cart bar matters for your store (it typically lifts conversion on longer product pages), that requires either a small custom code snippet added to the product template, or a lightweight app built specifically for it.

Is it worth fixing?

For most stores, desktop's default sticky layout is enough. It's worth adding a mobile sticky bar specifically if your product pages are long — lots of images, descriptions, or reviews above the fold.