fontSize property
The size of fonts (in logical pixels) to use when painting the text.
The value specified matches the dimension of the em square of the underlying font, and more often then not isn't exactly the height or the width of glyphs in the font.
During painting, the fontSize is multiplied by the current
textScaleFactor to let users make it easier to read text by increasing
its size.
The getParagraphStyle method defaults to 14 logical pixels if fontSize is set to null.
Implementation
final double fontSize;