Is there a method to add multiple properties to HtmlTextWriterStyle?
Under normal circumstances, you could use collection initializer to write your code this way:

var dynDiv = new HtmlGenericControl("Div")
{
    ID = "dynDiv",
    Style =
    {
        { HtmlTextWriterStyle.BackgroundColor, "Red" },
        { HtmlTextWriterStyle.Position, "absolute; left: 500px; top: 500px" },
        { HtmlTextWriterStyle.Height, "30px" },
        { HtmlTextWriterStyle.Width, "300px" }
    },
    InnerHtml = "New Object"
};


Unfortunately, this code won't compile, because CssStyleCollection doesn't implement IEnumerable, which is a requirement for collection initializers.