Understanding where the style rules are (in the style sheets) and which ones are seen in a web page (that’s the cascade) is critically important in knowing how to use CSS effectively and to leverage what it does to make great looking web sites. It’s what I spend a lot of time explaining in Practical CSS.
Cascading Style Sheets (CSS) is what gives life to a web page. It is the system, being developed by the World Wide Web Consortium (W3C), that allows us to define the appearance, the layout and typography – the look and feel – of a web page.
The very words “Cascading Style Sheets” define exactly what CSS is and how it works.
Style Sheets? In a web browser that’s a distinct group of rules used to set the style of a web page. In a web browser there are 3 style sheets just like you see in this image. The Browser Style Sheet, User Style Sheet and the Designer Style Sheet. Each of those style sheets have style rules that deal with setting a page’s background color, font size, family and color, padding, border and margin and so much more!!
Cascade? That’s the mechanism (it’s really an algorithm) built into every browser. It’s purpose is to rank the style rules in the style sheets and assign each style rule a value. The ones with the highest values result in style rules which are honored, meaning style rules that influence how a page looks.
See the Course Outline for more info.