This question already has an answer here:
In the Users page, the sub tab option is not selected with the last selected option. I mean the sub tab options as week/month/quarter/year/all under Reputation and reputation/creation date options under New Users and so on.
When inspect the sub tab elements, for the selected option the CSS class
is-selected is applied. But seems like there is no CSS code for the class.
When checking with the Profile page (there the selected tab is highlighted), the class
youarehere is applied for the selected tab. Replacing the
youarehere class name in the users page, the selected tab is displaying as expected.
The issue is in the all main and meta sites of the Stack Exchange.