CSS size is probably the last thing in the list of things to be worried about with a startup.
Bobby Juncosa

Look into it from a different perspective. My main competitors in SERP are https://www.odeon.co.uk/, https://www.cineworld.co.uk/ and https://www.myvue.com/. All of them are flogging the PageSpeed Insights test. Meanwhile, it is well known (https://moz.com/learn/seo/page-speed) that page speed has big impact to the SEO. Making the CSS smaller is part of the effort to make the website load faster and climb higher in the SERP.