The size of the IDE serial monitor window is adjustable by grabbing the edge of the window, but only down to a minimum.

The minimum width of the IDE serial monitor window is too large and it fills a large portion of the screen.
This behavior is new with 1.8.10 (or possibly earlier). I use mac os. The limits to the size of the window should be similar to the limits for the main IDE window.

The screen shot shows both windows at their minimum size.

Additional context

Additional reports

• IDE serial monitor minimum width too large #9633 (comment)