** If you have a relatively new phone, install True Silence v2 instead: https://play.google.com/store/apps/details?id=com.panic.silence **
Many manufacturers do not allow this with all volume streams and many other applications will only let you set one at a time. True Silence is the only one tap solution to the problem! It also remembers and restores your previous volume levels on second tap.
True Silence is lightweight, open source, and requires no permissions to run. It is also ad free! Please see the website if you would like to give feedback or contribute in any way.
Other programs can always 'unsilence' you. Android is just built that way, mind your apps. Also this is a widget, remember that you must add it to your home screen via long press.