I'm going to assume you are interested in something like this:
Arthur.
CssData css = HtmlRenderer.CssData.Parse("body{font-family:italic;background-color:Yellow;san-serif;font-size:100px;}", true);
Image m_Bitmap = HtmlRender.RenderToImage("<html><body><div><div>Hello World, Converting Html To Image!!!</div></div></body></html>", Size.Empty, new System.Drawing.Size(500, 500), Color.White, css);
m_Bitmap.Save(@"D:\Test.png", ImageFormat.Png);
Please invest the time in your code:- You used totally unrelated discussion to ask your question
- Your CSS is invalid, really not related to HTML Renderer project.
- In related previous discussion I pointed to relevant page: Generate image from HTML markup. If its unclear please let me know how to improve it.
- the sample code you provided contains unused code:
var img = HtmlRender.RenderToImage(File.ReadAllText(@"D:\html.txt"), 600);
Good luck,Arthur.