This test page of HTML elements shows how they look with YUI Base (and Reset and Fonts) applied.
YUI Reset neutralizes the browser-provided presentation of HTML elements. But a default presentation is often convenient, so YUI Base provides one that is consistent across browsers and operating systems. This example is a test page showing HTML elements with YUI Reset, YUI Fonts, and YUI Base applied.
Because CSS examples are susceptible to other CSS on the page, this example is only available in a new window at the above link.
All YUI 2.x users should review the YUI 2.8.2 security bulletin, which discusses a vulnerability present in YUI 2.4.0-2.8.1.