Steps to replicate the issue (include links if applicable):

• Use Vector-2022
• Go to a page with many sections, such as https://pap.wikipedia.org/wiki/Wikipedia:Portal_di_komunidat
• Scroll down on the page
• Notice how the active section in the ToC gets bolded in the ToC
• Keep scrolling down

What happens?:

• When you scroll past the lowest section title that is visible in the ToC, the ToC doesn't scroll with you, unless you actively scroll inside the ToC container

What should have happened instead?:

• When the section header in the ToC changes (e.g. when activaveSection() runs, it should also scroll the ToC to that section.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):