Start Small, Start Now (how to start with accessibility -- good for non-techie web people)
https://accessibility.umn.edu/start-small-start-now

WAI-ARIA basics
https://developer.mozilla.org/en-US/docs/Learn/Accessibility/WAI-ARIA_basics

10 Guidelines to Improve Your Web Accessibility
https://aerolab.co/blog/web-accessibility/

Writing CSS with accessibility in mind
https://medium.com/@matuzo/writing-css-with-accessibility-in-mind-8514a0007939