Preview with another theme
You may find the ThemeKey module useful.  This module allows you to define arbitrary rules to determine when to show each theme.  You can make as simple or as complex a configuration as you want.

From the module page, the following features are supported:


  
  individually-styled channels
  a front-page / "splash" screen
  a date/time-selected Christmas theme
  mobile themes for different auto-detected mobile devices
  special themes for "limited" or "old" browsers
  content, user, or role -specific themes
  indicating your environment (production, staging, testing, sandbox, … )
  testing your redesign safely on a live server
  


See the documentation for more details.