function matchHeight () {
    //check if browser supports the method
    if (document.getElementById) {
	//get offset height from opaque div
	var opheight = document.getElementById('main-opaque').offsetHeight;
	//set tranlucent div height to same
	document.getElementById('main-translucent').style.height = opheight+'px';
    }
}

//run function after page loads
window.onload=matchHeight;