Link to this javascript in the head of the iFrame content document (the child document).

// JavaScript Document if (window.parent.screen.height >= 700) { document.write('<link href="css/WideScreenStyles.css" rel="stylesheet" type="text/css">'); } else { document.write('<link href="css/NarrowScreenStyles.css" rel="stylesheet" type="text/css">'); }

Of course this could be used for redoing the styles of the iFrame contents based on any other property of the parent document as well. For example you could say

Parent.document.body.some.property= 'a value"

window.parent.screen.height