Hi Mikiya Sato,
There is no option to tell where to output style sheets added in the markup in relation to built-in style sheets. Since they are in the markup they are the first style sheet references, which exist in the style sheet collection; RadControls' and any other embedded style sheets are added at a later stage and so they appear after the ones in the markup.
Currently, you can explicitly add the style sheets of a control before the one in the markup. Of course, if you have lots of controls this will be a tedious operation, however it is the only way.
I hope this helps.
the Telerik team
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