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<!DOCTYPE html>
<html>
<head>
<style>
#text {
position: fixed;
top: 0px;
left: 0px;
background-color: #f00;
border-radius: 50%;
width: 100px;
height: 100px;
}
</style>
</head>
<body>

<div id="text">anal</div>

<script type="text/javascript">

var text = document.getElementById("text");

var pos = {
x: 0,
y: 0,
xvel: 5,
yvel: 0
};

setInterval(function() {
   pos.yvel += 1;

   pos.x += pos.xvel;
   pos.y += pos.yvel;

   if(pos.y + 100 >= window.innerHeight) {
      pos.yvel *= -1;
   }

   text.style.left = pos.x + "px";
   text.style.top = pos.y + "px";


   text.style.top = y + "px";
},50);

</script>

</body>
</html>