KnobStyle constructor
      const
      KnobStyle({ 
    
- double knobRadius = 0.08,
- double borderWidth = 0,
- GaugeSizeUnit sizeUnit = GaugeSizeUnit.factor,
- Color? borderColor,
- Color? color,
Creates the knob style with default or required properties.
The arguments knobRadius, borderWidth must be non-negative.
Implementation
const KnobStyle({
  this.knobRadius = 0.08,
  this.borderWidth = 0,
  this.sizeUnit = GaugeSizeUnit.factor,
  this.borderColor,
  this.color,
}) : assert(knobRadius >= 0, 'Knob radius must be a non-negative value.'),
     assert(
       borderWidth >= 0,
       'Knob border width must be a '
       'non-negative value.',
     );