"Telerik.Sitefinity.Resources.Themes.LayoutsBasics.css" should be added to a page whenever there is a layout widget in it. The set of css files in your second post should be added only when editing the page. The files which start with "Telerik.Web.UI.Skins" are needed by the Rad Controls on the page and the ones which start with "Telerik.Sitefinity.Resources.Themes.Default" are needed by Sitefinity.
Let us know if you need further help.
the Telerik team
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