How to make activity on top of all windows (as in google translate)?

Question

Android

Tell. How can I implement the appearance of an activity in the same way as it is done in google translate? Namely - a fixed size, translucency, (optionally - the ability to drag and drop).
An example of what I want to repeat (upper right corner. round G button):

Answer 1

Detailed tutorial https://medium.com/@rotxed/drawing-over-other-apps...