All platforms with Firefox: Globex Designs, makers of the popular Gmail Redesigned skin, have released a standalone Firefox extension which applies the style without Stylish (or Better Gmail and/or Better GCal). Download the extension to completely redesign your Gmail and Google Calendar with the latest and greatest style from Globex. Here's what the skin looks like.

Here's what Gmail looks like wearing the Redesigned skin:

And Google Calendar:

Since Globex will be maintaining this extension themselves, use it instead of Better Gmail or Better GCal to apply the style—it will be the most up-to-date way to get fixes and upgrades to the skin. Make sure you de-select the Redesigned skin in Better Gmail and Better GCal and in Stylish to use the official Globex extension. Google Redesigned is a free download for all platforms running Firefox.

Google Redesigned [Globex Designs]