In Sciter <frame> element may have content-style attribute defined. That content-style attribute takes URL of style sheet that gets applied on top of existing styles of the document: <frame src="some-child.htm" content-style="content.css" /> That content.css gets appended to the list of other styles of the some-child.htm as if that document has <link rel="stylesheet" type="text/css" href="content.css"> at…