Blazor (server) CSS isolation in Razor Class Library: .styles.css bundle generated but not served (404)

[guillaC]

Hello,

I’m building a Blazor Server solution with two projects:

• DeskUI -> Razor Class Library (Sdk=Razor, RazorClassLibrary=true, ScopedCssEnabled=true, GenerateScopedCss=true, PackageId=DeskUI).
• DeskUI.Demo -> Blazor Server app (Sdk=Web) that references DeskUI via .

Inside DeskUI I have components with .razor.css files.
During build, MSBuild correctly generates the scoped CSS files (.rz.scp.css) and bundles them into DeskUI.styles.css under obj\Debug\net10.0\scopedcss\bundle.

The issue:
When I run the Demo app and reference the stylesheet in _Host.cshtml:

<link href="_content/DeskUI/DeskUI.styles.css" rel="stylesheet" />

the browser always returns 404 Not Found. Other static assets from the RCL (like drag.js or images in wwwroot) are served correctly via _content/DeskUI/.... Only the DeskUI.styles.css bundle is missing.

What I’ve already checked:

• Both projects are part of the same solution.
• Demo is the startup project.
• UseStaticFiles() is enabled in Program.cs.
• PackageId matches the _content/DeskUI path.

Clean/rebuild doesn’t help.

The file exists in DeskUI\obj\Debug\net10.0\scopedcss\scopedcss\bundle, but it is not published to _content.

So the problem seems to be that the static web assets pipeline does not expose the generated .styles.css bundle from the Razor Class Library, even though it is created during build.

Has anyone else experienced this issue with Blazor CSS isolation in Razor Class Libraries (on .NET 10)? Is there a known fix or workaround other than manually copying the bundle into the host app’s wwwroot?

I would like to share my Razor library on NuGet, but as it stands this issue is really blocking me. If anyone has a lead, please let me know.

[oroztocil]

@guillaC Hello, thank you for contacting us.

To quote the docs:

For library components that use CSS isolation, the component styles are automatically made available to the consuming app. There's no need to manually link or import the library's individual component stylesheets or its bundled CSS file in the app that consumes the library. The app uses CSS imports to reference the RCL's bundled styles. The bundled styles aren't published as a static web asset of the app that consumes the library.

This in practice means that you should not reference the RCL's isolated CSS bundle directly. You only need to reference the app's style bundle itself, e.g.:

<link rel="stylesheet" href="@Assets["DeskUI.Demo.styles.css"]" />

This bundle automatically imports bundles from libraries that the app consumes.

[dotnet-policy-service]

Hi @@guillaC. We have added the "Needs: Author Feedback" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.