Get back old theme

Are you referring to an Office color theme or a document design theme?

Microsoft's terminology is sometimes ambiguous. Are you referring to an Office Theme (= the appearance of the apps themselves), to a Document Theme (= formatting and design elements defined in Office files) or maybe to the overall appearance of the operating system, that is, a Windows (system) theme?

Note that if you are asking about Windows themes, you should repost in the Q&A forum at https://learn.microsoft.com/en-us/answers/tags/824/windows-home. The Windows category has been retired in the Microsoft Community.

Hi, Colette Mena 

Have a good day !

I value your feedback, please mark it as an answer if it answer your question and click Yes to help me improve the support experience.  

It's so important for me to mark it as an answer. It's help me to have a good motivation forward.

I appreciate your patience with me.    
Looking forward to your response and have a great day ahead!!  
  
Best regards.  

Sting-Ng - Microsoft Community Support Specialist

Hi, Colette Mena 

Welcome to the Microsoft community. 

I understand how frustrating it can be when the theme changes unexpectedly. 

Typically, if your Office 365 applications (such as Excel, Word, etc.) have switched to a dark theme and you'd like to revert to the original color scheme, you can follow these steps: 

• You can also change the theme by going to**"File" > "Options" > "General" > "Personalize your copy of Microsoft Office."**Here, you can select one of the themes: "White," "Dark Gray," "Black," or "Colorful." After making your selection, click "OK" to save your settings. 

You can reference to: Change the look and feel of Microsoft 365 - Microsoft Support 

Based on your description, it seems that you have already tried to modify the theme via the General tab, but the problem still persists. In this case, you can try the steps to modify the theme throughthe account settings. 

If the problem still persists, then there may be a problem with the Office application itself, and you can try toreset Office in the registry and then modify the theme again to see the result: 

1. Press Win + R, type regedit and press Enter.
2. Navigate to the following path: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\UI Theme
3. Delete the UI Theme key.
4. Close the Registry Editor and restart the Office application.

Disclaimer: Modifying the registry or workgroups is usually geared towards advanced users, administrators, and IT professionals, and it can help to fix some problems, however, improper registry modifications can lead to serious problems. Therefore, please make sure to follow the steps below strictly. For further protection, make a backup of the registry before modifying it. For more information on how to back up and restore the registry refer to:How to back up and restore the registry in Windows - Microsoft Support 

If the above does not resolve the issue, it is recommended that you try repairing or reinstalling the Office 365 applications to ensure that all settings are restored to their default state. 

Let me know if this helps or if you need further assistance! Looking forward to any updates you may have. 

We look forward to your reply. We will continue to assist you if you any other question or based on the information you provide. I sincerely appreciate your patience and cooperation.     

If my answer is helpful, please mark it as an answer by Yes, which will definitely help others in the community who have similar queries to find solutions to their problems faster. 

Thanks and Have a good day!!! 

Best regards.      

Sting-Ng - Microsoft Community Support Specialist.