How does the browser set a scaled font size?

CSS allows us to set font sizes using 1 value.
If I scale an element with text in it the text will stretch vertically and/or horizontally to match the new scale.
I can scale an element vertically (el.style.scale = '1 2') and the font will stretch vertically so the text is very tall.

How can I make CSS cause the font to do that without scaling the element?
How can I convert scaled fonts to CSS font size properties?