Append stylesheet to iframe contents (e.g. Twitter widget) - this is filthy, but it works well when no other option is available.

Append stylesheet to iframe.js

$(document).ready(function(){ 
  setTimeout(function() {
        var iframe = document.getElementsByTagName('iframe')[0],
        iframeDoc = iframe.contentWindow.document;
        var otherhead = iframeDoc.getElementsByTagName("head")[0];
        
        var css = document.createElement("link");
        css.type = "text/css";
        css.rel = "stylesheet";
        css.href = "/SiteElements/Stylesheets/twitter-widget.css";
        
        otherhead.appendChild(css);
    }, 500); 
});

From the depths of the internet, and on behalf of others who learnt from this without saying anything, thank you.

I would like to say thanks also... saved a lot of time