How do I get that "buy" thing on my website, like CAINTÉ has on their product page?

[OneCap]

www.onecap.se 

https://cainte.se/collections/best-sellers-for-him-ny/products/silver-white-watch-1 

[Sweet_Savior_3]

Hello @OneCap 

Are you looking to add the sticky ATC bar to your website similar to Cainte.se ?

If yes, then it is a custom thing. You need to hire a professional to setup this to your store.

Thanks