V14: Remove user-defined.css

[iOvergaard]

Description

These files intended that we would place them in the StaticAssets RCL and developers could overwrite them in their projects.

We need to devise a different way to do this as you cannot just overwrite assets in an RCL.

[abjerner]

Any plans for an alternative?

I was playing a bit around with adding a bit of branding to the login screen and the backoffice, and ended up hijacking the route to the CSS file as it could be overwritten as suggested by the comment in the returned file.

For now this was just me testing what was possible, but we do have a bit of branding for some of our pre-v14 sites, and I'd imagine we would need these possibilities again. I also started a thread about my exploration and findings on Discord:

https://discord.com/channels/869656431308189746/1268501698620559461

I think an extension point for adding custom CSS files would make a lot of sense. Especially if one could specify a weight or an enum location (or both) in which the CSS file would be added - e.g. before Umbraco's CSS files (like with user-defined.css) or after page load.

[iOvergaard]

Hi @abjerner, sorry for only getting back to you now after all this time. We want to make it easier to add a stylesheet to the Backoffice than it is today. The user-defined.css file didn't work out since you had to do hijacking of the route, and it would just needlessly load the file anyway if you didn't. It goes against the principles of the Backoffice which says, you should only load the files you need.

It is supported to load a stylesheet into the Backoffice client even today, but there are a few hoops you have to jump through, namely: Register an entrypoint through a manifest and add a link tag to the header through javascript.

It makes sense DX-wise to make this easier, but I'm unsure what we need to do. We can easily make a helper function for entrypoints to add stylesheets, but from reading what you wrote here, I think we need to go a bit deeper and play around with some resemblance of what we had in the old backoffice with the css array in package.manifest, but with the addition of weights.

This calls for a discussion, which I will go ahead and start. Feel free to share your opinions here: #17049