Simple Javascript to allow an iframe to have it's parent css rules.

child.html

  <script>
    var parentStyleSheets = this.parent.document.styleSheets;
    var cssString = [];
    for (var i = 0, count = parentStyleSheets.length; i < count; i++)
    {
        var cssRules = parentStyleSheets[i].cssRules;
        if(cssRules)
          for (var j = 0, countJ = cssRules.length; j < countJ; j++)
            cssString.push(cssRules[j].cssText);
    }
    var styleEl = document.createElement('style');
    styleEl.type = 'text/css';
    styleEl.innerHTML = cssString.join("\n");
    document.head.appendChild(styleEl);
  </script>