Google Shopping CSS is a way to place shopping ads. CSS stands for Comparison Shopping Services and refers to the main search on the Google homepage. The introduction of Google Shopping CSS became necessary because Google was using the search results page exclusively for its own offer: Google Shopping. Other price comparisons (comparison shopping services) did not show up until much further down in the search results. The European Commission recognized this as unfair competition.
To level the playing field, Google pulled up the ad platform under the name Google Shopping Europe (GSE) as a price comparison site and opened it up to external price comparison sites, the Google CSS Partners. The result: for some time now, all shopping ads that appear in Google’s main search results have been part of a Comparison Shopping Service (CSS).
Google Shopping itself also acts as a CSS (“From Google”), participates in the bidding auction like the other price comparison platforms, and competes with other CSSs that place bids on behalf of merchants. However, in order to use its own price comparison in an EU-compliant manner, Google retains around 20% of your maxCPC bid as a margin. This will always reduce your bids by about 20% if you leave them on Google Shopping Europe. If you use a CSS partner for your ads, the margin is completely eliminated.
For Google users the difference is hardly noticeable, the only visible change is the added line “From ….” at the bottom of the ad.