Resizing window relative to screen size using PIXELS

Configuration Help & General Discussion
1

I want to resize my windows to not be blocked by MacOS's notifications, which are on the right side of the screen and 346 pixels in width.

I also want this to work regardless of my screen resolution (if I change my monitor resolution).

Fortunately, the notifications size is always 346 pixels.

However, in Custom Move/Resize Window, the options to size the width only show the

Absolute: new width x px
Relative to screen: new width x %

So I need to use Absolute.

How do I set the Absolute to screen size -346 px?