Multitasking at a new level: Google Chrome has learned to display websites in mini mode on top of other windows on Android

And other Chromium-based browsers

Chromium-based browsers like Chrome, Brave, and Edge are getting a new feature on Android that will make it easier to multitask and track web pages while using other apps. A new button will allow you to quickly collapse a web page into picture-in-picture mode. (PiP) — the tab will shrink to a small window that can be placed on top of other applications.

This feature is currently being tested in developer builds of Chrome and Brave. It is expected that it will be implemented in the stable versions of these browsers in the coming months. 

The tab collapse button can be found on the toolbar. The PiP window can be moved and resized according to the user's preferences. When you click on the PiP window, the site will expand to full size.