We just put in the 3.1 update, and the font size is way too large on the Admin portal. I’ve copied the ‘grey’ them to create a custom theme, but am having trouble locating the right place to change the font size. Where would I place the setting?
You’ll want to look at /static_3.1.1/css/base.css as that has all the style definitions. Most fonts are % based so you could actually in most cases use the browser to make it smaller without a theme, but otherwise just override the ones you want smaller by their class names in the custom theme css.
Using the developer tools in Chrom/Safari or Firebug in FF will let you easily find the class names you need.