W3C on accessibility: https://www.w3.org/WAI/fundamentals/accessibility-intro/
Making the Web Accessible and Web Content Accessibility Guidelines (WCAG) Overview
WAI-ARIA Overview
Web Accessibility in mind
Contrast calculator: https://contrast-ratio.com/
Good practices on accessibility: https://webaccess.berkeley.edu/resources/tips/web-accessibility
Checklist: https://www.a11yproject.com/checklist/#content