function login() {

	var feld_username = document.getElementById('username').className;
	var feld_password = document.getElementById('password').className;


	if(feld_username == 'i1') {
	document.getElementById('username').className = "i1_error";
	}
	
	if(feld_password == 'i1') {
	document.getElementById('password').className = "i1_error";
	}

}