I've only just started watching these vidoes, but they look to be really informative for people looking to take the dive into more advanced styling of their components.
I have a suggestion in the first video though. When creating custom class selector rules, the video mentions that the class won't be selectable from the style.classes dropdown menu, so you have to type it in manually without the psc-. This is the reason I always add (and recommend adding) a blank style class into the Perspective Styles for each and every custom class selector rule that you add into the stylesheet or CSS theming files. Otherwise, onboarding newbies onto a project just takes more time and it takes transparency and ease of use away from the developer.
This would be good to mention in the videos imo.
It would also be good to identify that you can open the dev tools directly in the Designer as well from the Tools menu.