2.1. Origins of a style sheet and the CSS cascade

Like an army general, your success or failure as a CSS developer will depend on your ability to consider many variables at once. Perhaps the most underappreciated variable in professional front-end web development is the presence of other style sheets in addition to your own. These additional style sheets are applied to your markup before your style sheet has a chance to affect it, so it behooves you to be aware of how these other style sheets can help or hinder your own work.