After the launching of Google+ project, Google completely changing looks of all products step by step. Today I found Gmail adopt complete new Google+ minimalist look. You can see it in the below screenshot.
In new look you will find floating ads at bottom, also it will eventually expand dynamically to accommodate different screen sizes and user preferences.
Google kicks two new theme, Simply go to Gmail Settings, click over to the Themes tab and select “Preview” or “Preview (Dense)” as your theme to try this entire new beautiful look yourself. At present some Labs features may look a little strange in the new themes, but google will roll out changes in the coming months.
So try the new Gmail theme and let me know via comment about your experience with the new Gmail themes.