Kevin Powell courses and YouTube channel
Kevin focuses mostly on CSS and HTML . His free courses start at the beginner level and include:
Kevin also has premium courses available for $50 to $250. Kevin also has a YouTube channel that focuses almost exclusively on CSS and HTML.
Wes Bos courses
Wes also has premium courses available for $44.50 and up. Wes (along with Scott Tolinksi) most the Syntax podcast. It covers front-end technologies. Wes also has a YouTube channel that focuses on front-end technologies.
Modern CSS Solutions website by Stephanie Eckles
Stephanie provides lots of great CSS content. This site features many great, focused tips on using CSS. smocss.dev is also Stephanie’s work with other focused CSS examples.
Miriam Suzanne is a leading CSS guru. She is an Invited Expert on the W3C CSS Working Group and her work can be found in many places, including here. Anytime you Google “CSS” and see Miriam’s name, click that link!
Google Chrome Developers YouTube Channel
Other YouTube channels worth checking out
9elements (especially Stephanie Eckles’ content)