One SEO professional asked John Mueller during a hangout about Lazy loading CSS. They explained that they had implemented a CDN for Lazy loading JS and CSS.
They found that this had increased their Core Web Vitals by at least 50 percent.
They just wanted to make sure that making such a change wouldn’t impact them negatively in any way.
John replied that it’s just fine to do things exactly like this, especially for CSS. It’s important, however, to consider how CSS does load because this could affect whether or not a page looks like it is mobile friendly to Google.
That’s something important to look out for.
Otherwise, John explains that it’s perfectly acceptable to use Lazy loading on CSS.
This happens at approximately the 32:22 mark in the video.