Are you curious which Theme is being used by a WordPress website?
There is an easy way to find out.
There are online Theme Detector Tools that find out the WordPress theme being used.
Online Detector Tools to find out which WordPress theme a site is using
The above websites scan the website and find if the theme being used exists in the WordPress Themes database. Aside from custom themes made specifically for the website, these tools could find out the theme with great certainty.