In page navigation doesn't allow highlighting last item on page (if it's small)

[kevindew]

If the last section on a page is not enough to full the viewport you can't get the header to be highlighted. This is particularly jarring if you link to a section.

For example if I go to https://content-api.publishing.service.gov.uk/#support the url will be changed https://content-api.publishing.service.gov.uk/#rate-limiting and the Rate Limiting header selected.

I'd expect that when I navigated to #support manually it would maintain that fragment and highlight the appropriate section