In college I was told to use 12pt font and now you and your browser must live with that.
Why?
My guess is that it's 1 pixel short of a typical 1.5x line height.
Standard line heights are usually 1.4.
When you use fixed font sizes like that browsers can't resize them based on the screen size/viewport. 12px fonts are really small and hard to read on high resolution screens.
That's false, px refers to CSS pixel, which is not tied to physical screen pixels.
It still renders excessively small on my lo-dpi screen. Absolute pixel sizing text is silly even if it is a phony virtualized unit.
They can still zoom them in, though. It's not like specifying a font size is an absolute value.