Gmail recently got it new design. The new design may look different, but the developers have not changed too much. There are opinions that refer to it as cleaner and easier to navigate.
The new application plan also brings new features such as the smart new email synthesis, and the postponement. Initially, you could choose the new design, but it has long been the default Gmail theme.
If you are one of those who disagree with the above, and are not happy with Google's change, below we will show you how to get the old app design if you have no problem using extensions / add-ons.
Using the old Gmail design in Chrome is pretty simple. There is an extension that you can install and will do everything for you. Install Gmail Classic Theme from Chrome Web Store and open your Gmail.
You will see the old Gmail design. Expansion will not remove any of the new features.
Firefox & Opera
The extension for the old classic Gmail theme changes the CSS that Google uses when it loads into your browser, and the extension developer guides you through the steps you need to do in Firefox and Opera without using it.
You'll just need to use another plugin that can change the CSS used by Gmail. The developer of Gmail Classic Theme recommends using it Stylus.
Download and install the extension in your browser. Then visit his page Github and copy the code in the file called Gmail.css.
Return to your browser and click on the Stylus extension icon.
In the small window that opens, click Manage. A new window opens.
Click Write New Style on the left and name the new css Gmail Classic. Once you've named your file, paste the copied CSS code.
Below this table, there is an option called 'Applies to everything'. Next to it, there is a plus button.
Click on this and, from the drop-down menu, select the 'URLs on this domain' option. In the domain field, type more at www.google.com, and click the Save top left button.
Visit Gmail and see the old application plan.
Gmail to other Browsers
You can use any other add-on instead of Stylus to change the CSS used by Gmail. The developer code will continue to work, and other browsers (Safari, Internet Explorer, or Edge) will need to find the right extension to edit the css.