1. Add allowTransparency=”true” property to the iframe
<iframe id="frame_one" src="iframe.php" allowTransparency="true">Browser not compatible</iframe>
2. Add background:transparent to it’s body tag or internal styles in the head section of an HTML page
<body style="background:transparent"></body>
or
<style type="text/css"> html,body { background: transparent; } </style>