Instructional Design Resources
Canvas Style Guide
This page details the CSS class names you can use in Canvas. The style guide is no longer being updated BUT after some researching, it seems the class names included will continue to work in Canvas for the foreseeable future. Note that form elements (e.g. ) are stripped from the content editor so you can't really use the HTML in the "Forms" section of the guide.
Tables Tutorial | WAI W3C
This page goes over creating accessible tables with multiple headers, different sized rows and columns, and other irregularities. There's some work that goes into making tables accessible and many LMSs do not use good defaults (for example, Canvas does not add a header row to tables by default).