fix toc highlight near bottom of page

[patrickdemers6]

Improved user experience by allowing clicking/highlighting of other sections near end of page, instead of defaulting to the last section.

Screen Recording

Before

https://github.com/slatedocs/slate/assets/12687723/a580381d-6e3b-4c04-b28f-3af015e78205

After

https://github.com/slatedocs/slate/assets/12687723/bc2ac78f-273e-4711-a3f8-2a24cdf00110

Fixes #1747