function getHeight() {
var blockUntenHeight= document.getElementById('blockUnten').offsetHeight/16;
var leftStretchHeight= document.getElementById('leftStretch').offsetHeight/16;
var rightStretchHeight= document.getElementById('rightStretch').offsetHeight/16;
var neueHoehe = blockUntenHeight - leftStretchHeight;
document.getElementById('backgroundLinks').style.height = neueHoehe+"em";
var neueHoehe02 = blockUntenHeight - rightStretchHeight;
document.getElementById('backgroundRechts').style.height = neueHoehe02+"em";
}