Gmail :New Look & Feel with Dense Theme
Apart from the new google services like Google + and notable design changes in it’s services, it seems to be Gmail too getting an new design interface.it might be a try out interface for the upcoming Gmail designs, however this try out theme is available in Gmail Theme options.
To gain the new Gmail interface ,Just change the default theme options with Gmail.Login to Gmail and click on the settings icon in the top left corner. Choose ‘Mail Settings’ option from the drop down menu. Click on Themes tab on the settings page.Scroll down on the themes page to find the Preview and Preview (Dense) themes. Choose any one of these themes and your Gmail interface will look just like your Google+ interface instantly.