Cannot customize display of alert titles

By following the "[Custom Alerts](https://dotnet.github.io/docfx/docs/markdown.html?tabs=linux%2Cdotnet#custom-alerts)" session, I created a token.json file and customized the alert title.

Despite changing the alert title, its default style is lost, and the side icon is missing. The alert itself is OK; it is just the alert title that is problematic.

I already had a custom template, but it was just for a small change on the footer partial; nothing else. We can assume everything else is default.

Do you have any ideas on whether this should be supported and where I could have a look?