This error occurs when a style uses a base whose compiled CSS is not part of the build. The compiler must place the CSS of the base before the style, so it cannot continue without it.
How to fix
- Import the base from its source module with a path that the bundler can resolve.
- If you write your own integration, keep the compiled results of all modules of the same build together.
A base whose type does not show its source is reported by unverified-style-base.