Lumen Learning provides instructions "Guidelines: Authoring Accessible Content" on how to add accessible original content.
I've highlighted a few sections:
Even though Lumen reviews their courses for accessibility, that does not mean all accessibility issues have been fixed. Several items which Lumen considers "supplementary materials" and "not strictly necessary for course completion or foundational to the learning experience" have accessibility issues:
Unless otherwise noted, these accessibility guides were created by Accessibility Librarian Amy Wolfe for CUNY and are licensed under a Creative Commons Attribution-Non Commercial-ShareAlike 4.0 International License. If you re-use, remix or link to this guide, it would be appreciated if you could notify the creator Accessibility Librarian Amy Wolfe.