I'm using a SharePoint DateTimeControl on a custom SharePoint page, while implementing theomplete behavior of the page I found that the DateTimeControl is not rendered properly on the page, the picker is opening but with no styles. Note that the control is working properly on the default SharePoint pages.
After a time of searching I found a solution by adding the following css (default datepicker stylesheet) reference inside the <head> tag of the iframe.aspx page.
<link rel="stylesheet" type="text/css"href="/_layouts/1033/styles/datepicker.css"/>
ifarme page location : %programfiles%\common files\microsoft shared\web server extensions\12\templates\layouts\iframe.aspx