How to customize SharePoint Office 365 theme
You can easily customize Office 365 theme (Logo, text color, ribbon color, top image)
Log in as Global admin in Office 365 Admin Portal Account and follow the below steps to customize Office 365 theme
1 Click on the top left App launcher then click “Admin”.
2 Click on Settings under Settings gear icon.
3 Select Organization profile tab and Click on Custom themes.
4 Now you can upload your company logo.
5 Navigation bar color, text color and more setting as you want to custom and click on “Save change ”button.
6 Now you can see the changes as you have done.