Understand which theme a page is using in Drupal 8

I am trying to do some theming for Drupal 8 and was trying to understand what would be the best way to understand what theme is being used on any given page. I remember using theme developer module in D7 and later doing dpm of the page array after theme developer started having issues.

1. Is there any helper module for D8, if so where can I learn to use them?
2. If there are no contrib modules, what other options do I have?

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