I asked the people who wrote my theme, OnePage with mythemeshop (not the other Onepage on WP) about the CSS, and they said:
“The first message (from PageSpeed-Try to defer or asynchronously load blocking resources, or inline the critical portions of those resources directly in the HTML) is just a suggestion to place more of your content above the fold but that is not crucial and not possible in these kind of sites. Your speed or SEO will not be affected.
You can try to optimize CSS delivery by using a caching plugin, it may give you better results.”
Maybe that is why my desktop speed dropped 20 points and my mobile site broke?