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.
As changes happen on SPO pretty much every week, it might not be a good practice to customize your branding through the master page when you are dealing with SPO. The reason is SPO's master page might be changed based on SPO new release. An alternative solution is to think about custom CSS and JavaScript injection through SharePoint CustomAction. You can reference PnP Partner Pack for site collection provisioning sample with responsive design.
If you really need to custom master page, you probably follow the exactly same way as SharePoint 2013 on premise environment to upload your master page and page layout. You can reference to How to: Convert an HTML file into a master page in SharePoint 2013 for detail information.
