About Bottom of the cascade

Always at the bottom of the cascade hierarchy is the browser’s own default style sheet. Typically,
the browser style sheet will have default settings for headings, paragraphs, lists, and all common
(X)HTML elements. It is the browser style sheet that makes links blue and visited links purple.
View any page in your browser that isn’t styled with CSS, and you will see the default browser styles.
So long as you define all the elements you wish to control, the default browser CSS will be
overridden. Remember that the default styling was designed for numerous reasons, specifically
legibility, accessibility, and common understanding. It is up to you to integrate these accepted
conventions into your designs, and seek to improve them, not disregard them.