First-party vs third-party stylesheets on Wix sites

Sites with first-party stylesheets stylesheet origin (first-party vs third-party) have a good LCP most often: 94%, against 94% of all Wix sites. Sites with third-party stylesheets CSS origin have it least often, at 93%.

First-party stylesheets is the most used: 100.0% of Wix sites.

Across the four LCP sub-parts in Chrome's field data, the largest gap between first-party stylesheets and third-party stylesheets sits in time to first byte (TTFB): 404 ms median for first-party stylesheets against 400 ms for third-party stylesheets. Overall median field LCP is 1.1s for first-party stylesheets (TTFB 404 ms, load delay 446 ms, load duration 110 ms, render delay 150 ms) versus 1.1s for third-party stylesheets.

React sets the stylesheet origin (first-party vs third-party) to first-party stylesheets on 100% of its sites, and 94% of React sites have a good LCP, against 94% of all sites.

FrameworkStylesheet origin (first-party vs third-party) on its sitesGood LCP

All Wix sites 5,621 sitesFirst-party stylesheets 100%Third-party stylesheets 34%94%

React 5,620 sitesFirst-party stylesheets 100%Third-party stylesheets 34%94%

First-party stylesheets Third-party stylesheets

Does the framework explain the stylesheet origin (first-party vs third-party) difference?

Almost every site with first-party stylesheets stylesheet origin (first-party vs third-party) is a React site, and almost every React site has first-party stylesheets stylesheet origin (first-party vs third-party), so the data can't tell first-party stylesheets stylesheet origin (first-party vs third-party) and React apart.

How cross-origin CSS files add DNS and TLS round-trips to the critical rendering path

Because external stylesheets block rendering by default, fetching a CSS file from a third-party domain (such as fonts.googleapis.com, cdnjs, or a widget CDN) stalls first paint behind a fresh DNS lookup, TCP handshake, and TLS negotiation. Across 5,621 sites (100.0%) with first-party CSS, good LCP is 94% (1.1s median), whereas across 1,909 sites (34.0%) with third-party CSS, good LCP drops to 93% (1.1s median).