Кнопка вверх вниз

<div id="ucodes"><i id="ucodes-f"></i><span class="ucodes-strelka"></span></div>

@media screen and (min-width:1200px) {  
#ucodes.up > .ucodes-strelka {width: 0;height: 0;border-left: 6px solid transparent;border-right: 6px solid transparent;border-bottom: 8px solid #fff;float: left;margin-right: 3px;margin-top: 2px;}  
#ucodes.down > .ucodes-strelka {width: 0;height: 0;border-left: 6px solid transparent;border-right: 6px solid transparent;border-top: 8px solid #fff;float: left;margin-right: 3px;margin-top: 2px;}  
#ucodes.up, #ucodes.down {left: 10px;top: 0px;width:50px;position: fixed;cursor: pointer;padding: 2px 7px;font-weight: bolder;text-align: center;background: red;z-index: 9999;border-radius: 0px 0px 3px 3px;color: #fff;border-bottom: 1px solid #133783;-webkit-box-shadow: 0 2px 2px -2px rgba(0, 0, 0, .52);font-weight: norma;font-size: 11px;}  
#ucodes.up:after {content:"Up"}  
#ucodes.down:after {content:"Down"}  
i#ucodes-f {position: fixed;top: 18px;bottom: 0px;width: 64px;left: 10px;-webkit-box-shadow: rgba(0, 0, 0, 0.521569) 0px 2px 2px -2px;border-radius: 2px 2px 0px 0px;background: rgba(159, 144, 178, 0.54902);border-bottom: 5px solid rgb(19, 55, 131);border-top: 1px solid rgb(58, 71, 97);}  
#ucodes i {display:none;}  
#ucodes.up i, #ucodes.down i {display:block;}
}  

var ucodesElem = document.getElementById('ucodes');
var pageYLabel = 0;
ucodesElem.onclick = function() {
var pageY = window.pageYOffset || document.documentElement.scrollTop;
switch(this.className) {
case 'up':
pageYLabel = pageY;
window.scrollTo(0, 0);
this.className = 'down';
break;
case 'down':
window.scrollTo(0, pageYLabel);
this.className = 'up';
}
}
window.onscroll = function() {
var pageY = window.pageYOffset || document.documentElement.scrollTop;
var innerHeight = document.documentElement.clientHeight;
switch(ucodesElem.className) {
case '':
if (pageY > innerHeight) {
ucodesElem.className = 'up';
}
break;
case 'up':
if (pageY < innerHeight) {
ucodesElem.className = '';
}
break;
case 'down':
if (pageY > innerHeight) {
ucodesElem.className = 'up';
}
break;
}
}