For all of the commenters doom posting that accessibility is so hard and expensive or that heaven forbid, this article expect web developers be able to Google and figure out topics on their own, there are plenty of resources!

Deque is world class in the a11y space, here is their open source library to run tests! https://github.com/dequelabs/axe-core
Even easier, Lighthouse is a usability tool in Google Dev Tools built on top of it, with lots of actionable accessibility audits! https://web.dev/accessibility-scoring/
The w3 has a bunch of specs on web accessibility! https://www.w3.org/WAI/standards-guidelines/

This is all very doable if you just put in the time.