Can't vouch for exactly how unconventional this is, but when I'm building a website I go through and do all of the HTML first, then CSS. Some I've seen do both

Can't vouch for exactly how unconventional this is, but when I'm building a website I go through and do all of the HTML first, then CSS. Some I've seen do both at the same time, create a header, then make the CSS, navigation, then CSS, little by little.