http://howrobotswork.wordpress.com/2013/08/16/creating-a-fullscreen-dialogfragment-with-a-custom-background/

The default Dialogs (or rather the DialogFragments) look pretty good in Android since Honeycomb, but the Holo look-and-feel doesn’t go well together with all app designs. Not to mention sometimes you need a fully different layout, a custom background color, or a semitransparent background with no grey dimming at all. We’re talking about Android, where (almost) everything is possible, so there is a solution for this problem as well.

Customizing a DialogFragment is a quite easy task. Create a class extending DialogFragment, and override the onCreateDialog method, which is responsible for creating the Dialog. Instantiate a Dialog, then make the following calls on the instance:

• requestWindowFeature(Window.FEATURE_NO_TITLE) – removes the dialog’s title
• getWindow().setLayout(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT) forces the dialog to occupy the whole screen estate
• setBackgroundDrawable() – sets the dimming drawable. This can be transparent, a solid color, a gradient or a custom drawable (even an image)
• create the layout and set it to the dialog using setContentView()

These four steps give you an empty fullscreen layout to play with, with the option to add a semi-transparent background, revealing the underlying activity. From this point, only your imagination is the limit; a good example of what can be achieved is the following screen, taken from an upcoming app:

You can find more on using and customizing the DialogFragment at the official developer site. Here is a short sample code illustrating a DialogFragment with a yellow background and an empty layout.