I had to make 3 search boxes.
But I think that is what you want.
It's a good start, but can I be a bit demanding?

If I search for a large number, it works. Example:
userID 459836 >
https://loyce.club/archive/members/45/459836.html < correct!But if I search for a small number, it doesn't use "0" for the directory:
userID 35 >
https://loyce.club/archive/members/35.html < incorrect! (this should have been
https://loyce.club/archive/members/0/35.html)
Edit: Just added bootstrap for design/format purposes.
It looks decent. Is is possible to strip all unneccessary data from
https://bitcoindata.science/css/bootstrap-grid.min.css? 49KB seems excessive

One more request: if I enter a number in your LoyceV Search Tool, I'd like to submit it be pressing "Enter", which currently doesn't work. The buttons can stay too

I didn't understand the old posts logic, but I can do it as well if I have more information
I'm guessing you're not the only one, and that makes it quite hard to use. I've explained it here:
Ideally, this should be included in the same search field: if someone searches for a low post number (say 25000030), it should give this link:
https://loyce.club/archive/oldposts/250/250000xx.html#msg25000030.
But if someone searches for a high number (say 5310200), it should give this link:
https://loyce.club/archive/posts/5531/55310200.html.
Can you pull that off?