When creating a book, the chapters and sub-chapters all overlap each other resulting in a jumble of text on the screen when viewed in Internet Explorer 11 on a desktop. Example:

This displays properly in Chrome, Firefox and Edge. It only happens in the Boost core theme, not the Classic theme. However, I also noticed it in themes based on Boost as they inherits the issue.

Reproducing the issue

1. Login as a Moodle administrator.
2. Ensure that the Boost theme is active (not an issue in Classic)
3. Create a new course.
4. Add a book to the course
5. Add 2 chapters to the book. Just a few words in the chapter titles and content fields are sufficient.
6. Save

Look at the automatically generated table of contents. You will notice that all of the chapter titles overlap each other.

Why is this an Accessibility issue?

Because it is only readable by a screen reader.

What I expected

I expected the table of contents to be readable, with each chapter on a separate line.