Sometimes I view a website which normally looks like it has been developed in a 2018 language like ASP.Net for example.
Most times it looks modern, and naturally strikingly beautiful.
However, sometimes the very same website looks like a Classic ASP format, without the use of modern spacing, fonts, etc.
This is not because the website has now become Classic ASP - it appears there is a glitch in the display timing and the "nice look" didn't catch up.
Clicking on a selection normally displays the website correctly again.

If I didn't know any better, I would think this website is actually written in classic ASP "with new clothes on".

I have a Classic ASP website (which looks like the website above when it is misbehaving).

How can I add that modern look, without reinventing the wheel and rewriting it in another language ?