A while ago, I wrote an SPFx Application Customizer that allows you to insert custom CSS on your SharePoint modern pages and posted about it.

The solution is now a sample in the SharePoint SharePoint Framework Extensions Samples & Tutorial Materials repo.

I received lots of feedback, comments and questions about the article so I decided to write an updated article to answer the most frequently asked questions.

I have since updated the solution to SPFx 1.8 and created a simple automated deployment script to (hopefully) reduce issues.

When migrating from SharePoint on-premises to SharePoint Online/Office 365, you may find that some users have a checked-out file called `spcommon[1].png`. If you ask users about it, they’ll have no idea what you’re talking about.

As it turns out, this isn’t a bug. It is possible for users to check-out this file without knowing they did it.