JSFiddle - React, Tailwind, and code Playground

HTML

<form>
<div onclick="move(this.children[0], function(p) {return p}), move(this.children[1], function(p) {return p})" class="aarde">
	<div id="zon"></div>
    <div id="maan"></div>
</div>
Days: <div id="dagen"></div>
</form>

<form>
<label><input id="snelheid" type="number"  value="30" oninput="speed(this)">Speed: </label>
</form>

<script>
var dagen = 0;
var multiplier = 30;
function speed($this){
  console.log($this.value);
	multiplier = $this.value;
    //alert(speedSetting);
	//return per;
}
function periode(bolletje){
	if (bolletje == 'zon'){var per = (multiplier*24/2);}
    if (bolletje == 'maan'){var per = (multiplier*24*29.5/2);}
    return per;
}
function step(delta) {
  elem.style.height = 100*delta + '%'
}
function animate(opts) {
  var start = new Date 
  var id = setInterval(function() {
    var timePassed = new Date - start
    var progress = timePassed / opts.duration
    if (progress > 1) progress = 1
    var delta = opts.delta(progress)
    opts.step(delta)
    if (progress == 1) {
      clearInterval(id)
    }
  }, opts.delay || 10)
   
}
function terugweg(element, delta, duration) {
    var to = -300;
    var bolletje = element.getAttribute('id');
    per = periode(bolletje);
	document.getElementById(bolletje).style.background='transparent';
	animate({
		delay: 0,
		duration: duration || per,
		//1 sec by default
		delta: delta,
		step: function(delta) {
		  element.style.left = ((to*delta)+300) + "px"   
		}
	});
    if(bolletje == 'zon'){
    	dagen ++;
    }
    bolletje = element;
    document.getElementById('dagen').innerHTML = dagen;
    //setInterval(function (element) {
    setTimeout(function (element) {
		move(bolletje, function(p) {return p})
	}, per);
}
function move(element, delta, duration) {
	var to = 300;
	var bolletje = element.getAttribute('id');
    per = periode(bolletje);
    document.getElementById(bolletje).style.background='yellow';
	animate({
		delay: 0,
		duration: duration || per, 
		//1 sec by default
		delta:...

CSS

hr{clear: both;}
form{display: block;}
form label{width: 300px; float: left; clear: both;}
form input{float: right;}
.aarde{width: 300px; height: 300px; border-radius: 150px; background: url('https://tijnvanwinden.nl/img/aarde.png');}
#zon{width: 40px; height: 40px; background: yellow; border: 2px solid yellow; border-radius: 20px; position: relative; margin-left: -20px; top: 120px;}
#maan{width: 30px; height: 30px; background: yellow; border: 2px solid yellow; border-radius: 16px; position: relative; margin-left: -15px; top: 115px;}