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Cascading is the process of combining different stylesheets and resolving conflicts between CSS rules and declarations. There is 3 rule in declaration rule; Source Order and Specificity and Importance. Author Stylesheet is an original sheet from the web page that you request via the internet. Browser Agent Style sheets override browser stylesheet. When you don’t want to default CSS style from Browser you need to use reset CSS. The goal of a reset CSS is to reduce browser inconsistencies in things like default line heights, margins and font sizes of heading.