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

A pixel is a single dot on the screen. Your example sets the element named header with no padding or margin. To understand this you'll also need to understand the CSS box model for page layout.