If you get bored with the default theme of your Office desktop apps, you can change the color and background to make it more personalized. This is simple and requires only a few simple steps, so we'll get started.
Changing Office color theme through app options
By default, Office uses the so-called "colorful" theme. This theme gives the title bar the color of each app. For example, Word is blue, Excel is green, PowerPoint is red and so on. In addition, you get a standard light gray background and ribbon, as well as a white content area.
You can change the theme from any Office application. These changes will be made in all your Office apps.
Open any Office application. This example uses Word.
Click the File tab at the top left corner of the ribbon.
On the left side, a window is displayed with various options. At the bottom of the window, select "Options."
In the Word Options window on the left, make sure the General tab is selected. On the right side, you will find the section titled "Personalize Your Copy of Microsoft Office ". Here you can change your office background and theme.
You have four theme options: Colorful, Dark Red, or Black. Select the theme you want to use.
If you want to change the Office background, you have some choices:  No background (default)
 05] After selecting the desired theme, click "OK" and you're done!
Unfortunately, Microsoft has not provided a preview of the topics with this option, so you need to repeat these steps to see each one. If you are not happy with it and are using Office 365, you can change the theme using the Account Settings, which will preview it.
Changing Office color theme through Account Settings in Office 365
Back In the app you are using, select "File" and then "Account" in the displayed area.
Your account information will be displayed. Select the menu under "Office Background" or "Office Theme" here, navigate through the different backgrounds and themes with a live preview and select the ones you want.
You will see a live preview while you go.