Eric White's Blog

I don’t know of any examples that give guidance / resources that show how to accomplish this.

With regards to writing C# code using the Open-Xml-Sdk, I personally prefer to generate the markup directly, and not use the strongly typed classes in the Open-Xml-Sdk object model. I prefer to use the LINQ to XML API.

My recommendation to you: I suggest writing the markup directly, and not using the strongly-typed OM. Since you have found examples of what is required when generating the XML directly, you are on the path to success.

Fifa, I do not see the correlation to generating conditional formatting in Excel.
Leebean, I am working on the same thing at the moment. From your post, you have successfully built a stylesheet. I have found a few links that are helping me. The key thing I got from this article was that entries for DifferentialFormats and TableStyles must exist to get the completed spreadsheet to open. I have been working on trying to flesh that out with official details for a few days. The pertinent code is:

    DifferentialFormats differentialFormats1 = new DifferentialFormats() { Count = (UInt32Value)0U };
    TableStyles tableStyles1 = new TableStyles() { Count = (UInt32Value)0U, DefaultTableStyle = "TableStyleMedium2", DefaultPivotStyle = "PivotStyleMedium9" };

...

    stylesheet1.Append(fonts1);
    stylesheet1.Append(fills1);
    stylesheet1.Append(borders1);
    stylesheet1.Append(cellStyleFormats1);
    stylesheet1.Append(cellFormats1);
    stylesheet1.Append(cellStyles1);
    stylesheet1.Append(differentialFormats1);
    stylesheet1.Append(tableStyles1);
    stylesheet1.Append(stylesheetExtensionList1);
    return stylesheet1;