Office365 admins can change the themes of their tenant. They can customize the navigation bar, change the colors other than the default. In order to do these changes to your tenant follow these steps.
1. Log in to your account with your email and password.
2. Go to Admin Center.
3. Select Company profile from the menu on the left side.
4. Click Custom theming.
5. Now here you have theme options like changing the logo, adding any clickable logo URL, Changing the background image, which is the background of the navigation bar and changing the colors for text links, and icons.
We suggest you be experimental with these options and adjust colors as you like because Look and feel matters a lot.
You can add an image as background wallpaper but the image must be less than 15kb of size.
6. You can always reset the default settings by clicking remove custom theming.
7. Here you do have a checkbox to prevent users from overriding the custom theme with their own theme, which can give you a little bit more control over the user behavior. click save button.
So you can change any or all of these features just keep in mind that there are somewhat image requirements for the logo and the background image. If you don’t have images that fit these requirements, we would recommend you to check with your marketing or branding team in the organization then they can work with to get you an image that meets those requirements.
Disclaimer: Sometimes it takes a few minutes for changes to take effect essentially across the entire tenant so if you right now are to look at your outlook page and you don’t see those changes that do not necessarily worry. They might take a few minutes to apply.