In MIS project I learn about Gmail, so I create my own Gmail and I started to design it . now I will show you how I add theme in my Gmail to like nice. 

first of all I enter my Gmail and it is without any theme:

Than I press on the setting :

After that I press on themes:

When you press on themes you will see the page full of  beautiful theme and I will choose Zoozimps theme :

When you press on the theme it will ask you about your city :

Finally the theme will loading and it shows like this:

I hop you learn from my this page.