Learning Front End Resources for Back End Dev - eviltoast

Any ideas what modern resources are useful for back end devs to learn modern front end development? I’m decently familiar with the basics of html, css, js, but don’t really have experience with frameworks beyond basic bootstrap v3/v5, a smidge of react, some angular 1, etc. Kind of a smattering of tools but without real confidence to wield them in anger, you know? Hopefully this post can be helpful for other design challenged programmers.

Edit: extra resources on accessibility and security would also be much appreciated!