File: geoportal\catalog\skins\lookAndFeel.jsp
The link to the tundra.css file of the JavaScript API is hardcoded and refers to the serverapi.arcgisonline.com page:
<link rel="stylesheet" type="text/css" href="http://serverapi.arcgisonline.com/jsapi/arcgis/2.0/js/dojo/dijit/themes/tundra/tundra.css">
It should refer to the JS-API resource that is configured in the gpt.xml. The css-link should also be placed in the ApplicationConfiguration context.