Here is a guide I just came across that seems to be a quite extensive resource for advanced HTML & CSS web development. It appears that the guide is sectioned into lessons, where a new lesson is posted each week. So you should be able to follow along at our own pace over time. From the first few lessons that I’ve read so far it seems to be a fairly good guide for somewhat advanced front-end web development work.

Check it out here: An Advanced Guide to HTML & CSS (learn.shayhowe.com/advanced-html-css)