CSS: How Large is a CSS Pixel?

CSS: How Large is a CSS Pixel?

px, in practice, is 1/16 of default font size of a device.

px is defined as reference pixel, which is a visual angle of 0.0213 degrees. This means, the larger the screen, the larger is 1px.

px originally was the same size as a physical pixel of desktop displays in the 1990s.

CSS Spec on What is a Pixel