Hi Zhi Jun,
I have not seen such appearance problems with the RadPrompt dialog box, yet similar issues are usually due to some custom CSS on the page that is affecting the RadWindow, too. Global rules like td, li, ul, table, etc. can break our controls. Could you try removing all custom CSS from the page to see if the issue persists? If not - readding the rules piece by piece should show you the offending one so you can make it more specific. If you have some custom code related to handling the FileExplorer dialogs - could you try disabling that to see if this is where the issue stems? If neither of this yields a resolution could you post here the minimal markup that results in this behavior so we can inspect it?
the Telerik team
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