Gone are the days when typography within a web page meant choosing sans-serif over serif. What used to be done with Adobe Flash can now be done with CSS. Breaking free of the browser’s fonts and being able to use custom fonts freed up web designers to use the subtleties of type design. The CSS calc notation allows the type to fill space the way the designer wished. The measurement units, vw, vh, vmin and vmax, allow the designer to create work that is responsive to the size of the viewport.
The blog, Made By Mike, helps explains how to use the calc notation: Precise Control over Responsive Typography.
CSS Tricks | A Couple of Use Cases for Calc()
David Walsh | Demo: CSS calc
W3C | Calc() Specification
Six Revisions | A Quick Overview of CSS calc()
Can I Use | Support for the calc() notation in browsers