What is a pixel (px) in CSS?

Question

I am reading an ASP.NET book and it refers to CSS files and talks about pixels. But I never understood it from a resolution, layout, etc. point of view. For example, what does t

Answer 1

It means a dimension, measured in pixels on-screen. E.g.

width: 200px;

means an element is 200 pixels wide.

A pixel is a "PICture ELement", meaning one coloured dot on the screen, probably much like the period at the end of this sentence.