CssSyntaxError unknown word

Got this strange exception. It’s unclear where there error happened and which word exactly is unknown. Any tips?

{
    "name": "CssSyntaxError",
    "reason": "Unknown word",
    "file": "/inline",
    "source": "1",
    "line": 1,
    "column": 1,
    "message": "Error while parsing 'inline' CSS style sheet.\n/inline:1:1: Unknown word",
    "input": {
        "line": 1,
        "column": 1,
        "source": "1",
        "file": "/inline"
    }
}

It’s useful to know what you did to get the error. Anyway, quick search says it happens on package build and most likely the reason is related to loaders

loaders didn’t change and stay same since start of the project