Have you ever updated your theme by replacing, or simply overwriting your old theme files? Well, when we edit themes we tend to add many custom styles that are supra-theme. Maybe there are styles for a plugin (such as my Post Information Plugin) that you want there regardless of what theme you have selected. Well, I have the fix for you.

1. Download the plugin
2. Activate
3. Then your styles under Presentation » Persistent Styles.

I should warn you that the style sheet will be printed after your primary sheet. I would advise on only adding non theme dependent styles, because it will throw off your CSS inheritance.

Have fun!