Looks like am email era got changed since Hotmail becomes Outlook and Google has introduced new interface of Gmail which is more user friendly and professional. Once you login to your account you would see a tab on right corner of the screen, just click to revamp your appearance towards new Gmail look. The appearance of your emails are categorized as Comfortable, Cozy and Compact and also the addition of HD themes under settings tab. A few HD themes are available on your Gmail account and still the old themes exists some of them are discontinued.
In-order to enable HD themes click settings (gear type icon) on right corner and select the desired HD theme from the options.
Click on Themes and you will be redirected to new gmail themes page having color themes, HD themes and classic themes.
Now select the theme under HD Themes tab and google will instantly apply to your account. These themes may vary from mine according to your location.