CSS is a style sheet language used for describing the presentation of structured documents (such as HTML pages) to a user. It is a cornerstone technology used by most websites to define their layout, design, and styles. CSS allows control over text formatting, page layout, and interactive forms.

1. 8. CSS
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E-learning and the science of instruction
Miles Berry
20 November 2013

4. http://www.codecademy.com/curriculum/uk