A Comparison Shopping Service (CSS) is a website that displays product offers from online retailers and then sends users to the retailers’ websites to make a purchase.
CSS with Google Shopping
Lyst acts as a CSS through Google Shopping, which is available in the European economic area and Switzerland. Within this service, CSSs (like Lyst) place product ads on behalf of a merchant. Google Shopping CSS began in June 2017, when the European Commission antitrust fine opened the landscape for Google CSS to allow non-Google partners like Lyst to run Google Shopping activity themselves.
This 1 minute video provided by Google helps to explain further how CSS functions.