Styles vs Themes

What is the major difference between Themes and Styles?

The reason I ask this is because it seems every theme template I download I have to actually mess with my styles in order to make the admin pages look similar to the theme, for my authors.

What I’d really love is a theme and style package I could download so that when authors log on to my site, they aren’t suddenly feeling like they’re at “Kubrick” when they should be at my site’s theme.

Any ideas?