I tried to design my personal website to be accommodating to users on slow connections (e.g. Tor, mobile) when rendering CSS. To avoid the page jumping when the CSS file is finally loaded, I generate a small chunk of CSS from the main CSS file, and inline it into the HTML which produces the proper page structure.
I don't use fancy, expensive CSS frameworks to do it; just a little bit of awk to grab flagged CSS blocks and sed/tr to slim it down a bit.
Mike Gerwitz's personal Mastodon instance