A single font can reference many different files with different
outline weights and styles:

The weight property specifies the weight of the outlines in
the file as an integer multiple of 100, between 100 and 900.
These values correspond to the FontWeight and can be used in the
fontWeight property of a TextStyle object. 
For example, if you want to use the RobotoMono-Bold font defined above, 
you would set fontWeight to FontWeight.w700 in your TextStyle.

    Note that defining the weight property does not
override the actual weight of the font. You would not be able to
access RobotoMono-Bold with FontWeight.w100, even if its weight
was set to 100.