aspnetcore/test/WebSites/HtmlGenerationWebSite/appRoot.css

body::after {
    display: block;
    background-color: #ff0000;
    color: #fff;
    font-size: 1.2em;
    margin-top: 2.4em;
    content: "ERROR: Stylesheet 'appRoot.css' was loaded from outside webroot!";
}