Jen Kramer is a US web developer and one of the longer-running Frontend Masters instructors, focused on HTML, CSS, and the foundations of front-end development. She has previously taught web development at Harvard Extension School and is widely respected for the depth and patience of her introductory CSS material.
Her CourseFlix listing carries two Jen Kramer courses: Web Development Project — Personal Portfolio Website (a project-based course building a complete portfolio site from scratch) and Getting Started with CSS, v2 (the foundational CSS curriculum for working developers).
Material is paid; Jen's courses are primarily distributed through Frontend Masters on the original platform. Courses are aimed at developers building real CSS competence rather than copy-pasting from Stack Overflow.