Using YUI Fonts CSS, specify font size using the provided percentages. (For example, 77% renders at 10px.) By using these percentages you get accuracty across A-grade browsers while still allowing IE users to zoom their font size.
With YUI Fonts CSS in place, define font sizes using the percentages found in the documentation and on the cheatsheet. For example, 77% renders as 10px; 138.5% renders as 18px.
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.