As we outlined previously, WordPress 3.8 includes design and user experience refreshes to the Admin area, and the theme previews are also getting some attention.
Less Text Clutter and Larger Screenshots
The functionality of the themes list and previews are mostly unchanged except for the visual experience. When navigating to Appearance-->Themes, you'll now see larger screenshots of your active theme as well as the themes you have installed.
You'll also see that the description and theme-specific links (like Widgets and Header options) have been relocated. You now get a Customize button in the upper right of the screenshot image that opens an overlay window containing the description and relevant theme management links.
Larger Description Area
After opening the theme preview in the overlay window, you'll notice that there is significantly more room to the right of the theme screenshot for the description. A nice touch is also the addition of scroll capability.
Smart theme authors should utilize this to write better formatted descriptions and also to promote any links that are relevant to the theme or their own sites. Hint hint...marketing opportunity.
Theme Search Location
A small, but effective user experience change is the location of the theme search input field. Searching installed themes is probably not something that most WordPress admins do regularly, but if you're one of those people that like to test various themes or change them often (seasonal perhaps), then this will definitely save you time.
A nice touch is that the search is also now predictive, meaning that the results are filtered as you type. You can see an example of that in the image below as I searched the keyword twenty and only see the built-in themes that come with a default install.
Watch the Video to See Theme Previews in Action