In July, the Google team showed a preview of Gmail new look, and now they have rolled out to users. You can switch to new look - they will display a button to do this.
According to Google Blog, - The detailed information is as below.
Today, we’re giving you an in-depth look at the new design. If you like what you see, over the next few days you’ll be able to switch to the new look by clicking on "Switch to the new look" in the bottom-right of Gmail.
- Elastic density
- Streamlined conversations
- New HD themes
- Smarter navigation
- Better search
Source : Google Blog