We created an HTML file with Office Fabric UI to make it responsive. Our intention is to integrate the HTML file we created with O365 SharePoint site and make it as our Intranet Home Page.
So, please let us know how to replace the default Master Page with our custom file. Any pointers to appropriate pages would be very helpful.
Account Info: Office 365 Business Essentials with SharePoint Online (Plan 1).
Thanks in advance.