How to get the zeroth time for the current day?

I am trying to find a sail expression that will return the current day's timestamp at the first second of the day.

For example:

now() returns 11/15/2021 4:39 PM EST

Looking for something along the lines of: 

myFunc(now()) returns 11/15/2021 12:00 AM EST

I tried 

now()-hour(now())/24-minute(now())/(24*60)-second(now())/(24*60*60) but it returns 11/14/2021 7:00 PM EST(Date and Time)

Any help will be appreciated,