When interested in non-blocking CSS search for: “filamentgroup loadCSS”.
But also just look at the amount of external requests, about 15 for CSS and about the same amount of javaScript files included (, and the site is not on http2 yet as far as I can see, so no benefits there).
Optimisation is tough when you have to do it after the fact. Best is to keep it in mind from the very beginning and make it a sport to concatenate those scripts and styles in two single files, and/or limit those plugins only for the webpages that actually uses them, and maybe inline them when there small and are only used on that one page (limited benefits from cache in that case).
