
Hello @Zara ,
Welcome to Q&A Forum!
You can see the HTML page corresponding to the default Master Page by using the SharePoint Designer.
Please follow the steps:
1.Open the SharePoint Designer as a site administrator
2.Click Master Pages
Based on Sharepoint security considerations, we recommend that you do not directly modify the default Master Page, but create a new Master Page directly and set it as the default Master Page.
Here are two good articles for your reference:
- How do I edit a master page?
- Steps To Create Custom Master Page In SharePoint 2013 Using Design Manager
Note:
Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
Thanks,
Echo Du
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