Při

<div id="right_slider" onload="myfunction()">

<script type="text/javascript">
	function myfunction() {
	    var elmnt = document.getElementById("content");
	    var txt = "<style> #right_slider {height: " + elmnt.offsetHeight + "px;} </style>";
	    document.getElementById("vypis").innerHTML = txt;
	}
</script>
<div id="right_slider" onload="myfunction()"> <!-- dopočítat výšku javascriptem! -->
	<p id="vypis"></p>