generateHtmlFromXmlUsingXslt

private string GenerateHtml(string xml)
{
    var doc = new XmlDocument();
    doc.LoadXml(xml);

    return TransformXml(doc);
}

private string TransformXml(XmlDocument doc)
{
    var transform = new XslCompiledTransform();
    if (doc.DocumentElement == null)
    {
        throw new Exception("blablabla");
    }

    using (var reader = new XmlNodeReader(doc.DocumentElement))
    {
        using (var stringReader = new StringReader(EmbedCssIntoXslt(viewModel)))
        {
            using (var resourcesReader = XmlReader.Create(stringReader))
            {
                transform.Load(resourcesReader, new XsltSettings { EnableScript = true }, new XmlUrlResolver());
                using (var writer = new Utf8StringWriter())
                {
                    transform.Transform(reader, null, writer);
                    return writer.ToString();
                }
            }
        }
    }
}

private string EmbedCssIntoXslt()
{
    var xDoc = new XmlDocument();
    xDoc.LoadXml(Resources.text); // point at your .XSLT
    var styleNode = xDoc.CreateNode(XmlNodeType.Element, "style", null);
    styleNode.InnerText = Resources.textStyle; // point at your .CSS
    xDoc.SelectSingleNode("//head")?.AppendChild(styleNode);
    return xDoc.InnerXml;
}