"This is part of a Google-wide effort to bring you an experience that’s more focused, elastic, and effortless across all of our products." Says Gmail Blog. You can slowly notice the changes in the future as Gmail team apply the changes.
We’re kicking things off with two new themes for you to try out as a sort of sneak peek at what we’re up to. Starting today, you’ll see the “Preview” and “Preview (Dense)” themes in the Themes tab in Gmail Settings. Why two themes? Our new interface will eventually expand dynamically to accommodate different screen sizes and user preferences, but until then you can pick the information density that you prefer.
A preview of Gmail’s new look - Official Gmail Blog
