Question

Using the CSS font-size property, one can specify the size as a percentage. What does this percentage refer to?

Answer 1

The percentage refers to the size percentage of the elements parent. I think the default browser font size is 14px, so:

  p{ font-size: 100%; } /* 14px */
  p{ font-size: 85%; } /* 12px */

It starts to get a little more complicated if you have this:

   <style type="text/css">
        div{ font-size: 20px; }
        p{ font-size: 80%; } /* 16px */
   </style>

   <div>
       <p>Some Test</p>
   </div>

Since I set a pixel size for the parent div, and a percentage size for the child paragraph, the child paragraph uses the parent pixel size as the base measurement.