I have found myself guiding traditionally non-web-based developers doing mostly intermediate front-end tasks. The discrepancy in skills and knowledge of CSS and how to properly use it between developers means I am spending a lot of time going over things such as pseudo elements, flex-box and css grid amongst others, and I am running short on time for my own work.

Im looking for any intermediate/advanced resources or courses to point others (and myself) towards when they are trying to get their head round some of the newer, less used or less well known parts of CSS, as well as a solid foundation.

Free courses preferred, although good paid resources are an option. Thanks!