function swapDIVs() {
    if (document.kontaktform.rueckruf.checked == true) {
            document.getElementById("disabled_rueckruf").className = "active";
            document.getElementById("enabled_rueckruf").className = "disabled";
        }
    else {
            document.getElementById("disabled_rueckruf").className = "disabled";
            document.getElementById("enabled_rueckruf").className = "active";
        }
}