What you can customize: You can personalize your ribbon to arrange tabs and commands in the order you want them, hide or unhide your ribbon, and hide those commands you use less often. Also, you can export or import a customized ribbon.
What you can’t customize: You can’t reduce the size of your ribbon, or the size of the text or the icons on the ribbon. The only way to do this is to change your display resolution, which would change the size of everything on your page. You can’t change the colour of the ribbon, or its icons, but you can change the colour scheme that Office uses throughout.
When you customize your ribbon: Your customizations only apply to the Office program you’re working in at the time. For example, if you personalize your ribbon in Word, those same changes won’t be visible in Excel. If you want similar customizations in your other Office apps, you’ll have to open each of those apps to make the same changes.