Before You Begin
Opening the Inbox is like walking into your office: you're going to be there for a while.

The default Theme in Office 365 is very plain. You can customize the Theme if you wish.

Try It: Change the Theme
Go to the Office 365 portal:
https://portal.microsoftonline.com.
Please log in.
Go to Outlook->Inbox->Options.
Select a Theme.

What Do You See? When you click on a Theme, it will be applied to the Inbox. Cheers!

OK, Let's get going...

Outlook->Inbox->Options