Quirky and unexplained behaviour

@sirclickalot, it looks like you are building a really interesting website!

Could you disable Javascript aggregation? That would facilitate investigation.

Ah yes, good idea.
DONE.

Thank you for you comment there; after 35 years in teaching, you could say that this WIP site is the culmination of a life's work!

More seriously though, it's an effort to provide a single place where students and teacher alike can get access to highly-scrutinised teaching and learning material relating to Computer Science.

Along the lines of this little story: https://sirclickalot.co.uk/assets/the-bit-by-bit-project

The scrolling is generated by something that sets the focus on this element in the page :

You can press the Shift key on Chrome to display the focus outline.

So it's most probably not related to ToC.js

Brilliant, thank you!