The blog post that you are referring to is using jQuery to replace the content of the sliding pane's tab with custom text and change the default rendering of the element and uses CSS to rotate the text. It might seems that the provided solution might seems to work at first, however, it is using static text and size for the tabs and this is not recommended.
The root of the problem is that when the text inside the sliding pane's tab is rotated using CSS the margins and the paddings of the element are not processed properly and RadSplitter cannot calculate the size the tab. That is why we recommend using images to produce the same appearance under different browsers.
In the the forum thread that I linked in my previous answer you can find a sample solution on how to dynamically generate image to be used for the Tab's.
the Telerik team
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