Color contrast is also important.
Like actually putting a readable header on the page. ('^_^)
I did some professional services work years ago, very early in my career for a public-sector client that wanted accessibility features given absolute care and attention.
It really gave me some perspective and I've tried to be conscious of it ever since; though I'm purely back-end nowadays so it doesn't apply as much.
What's fun is making an app that explicitly requires well sightedness (scanned documents), and meeting accessibility requirements for literally everything in the app beyond that.
Aside: I wouldn't mind seeing a library where you can give a text weight and text color, with the background color you want to use, but it returns the closest background color that will meet accessibility/contrast requirements.