I'm trying to fix my table header once it is scrolled down that it fixed at the top position.
I've managed to fix the header by making a javascript to detect the scroll position and then apply css to make the position as fixed at the top
But the column sizing of the header become lost, apparently it become smaller.
I will appreciate if someone able to help on this?
<html>
<header>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.0/jquery.min.js"></script>
<style>
.scroll{
   position: fixed;
   top: 0 !important;
}
#myDIV{
   background-color: #ccc;
}
header{
   height: 100px;
}
footer{
   height: 2000px;
}
</style>
</header>
<body> 
<table style="width:1900px" >
        <thead id="myDIV">
            <tr>
                <th style="width:25%"  >Column1</th>
                <th  style="width:25%" >Column2</th>
                <th  style="width:25%" >Column3</th>
                <th  style="width:25%" >Column4</th>
            </tr>
        </thead>
        <tbody >
            <tr>
                <td style="width:25%" >aaaaaaaaaaa</td>
                <td style="width:25%" >bbbbbbbbbbb</td>
                <td style="width:25%" >ccccccccccc</td>
                <td style="width:25%">ddddddddddd</td>         
            </tr>
            <tr>
                <td>aaaaaaaaaaa</td>
                <td>bbbbbbbbbbb</td>
                <td>ccccccccccc</td>
                <td>ddddddddddd</td>
            </tr>
            <tr>
                <td>aaaaaaaaaaa</td>
                <td>bbbbbbbbbbb</td>
                <td>ccccccccccc</td>
                <td>ddddddddddd</td>
            </tr>
            <tr>
                <td>aaaaaaaaaaa</td>
                <td>bbbbbbbbbbb</td>
                <td>ccccccccccc</td>
                <td>ddddddddddd</td>
            </tr>
            <tr>
                <td>aaaaaaaaaaa</td>
                <td>bbbbbbbbbbb</td>
                <td>ccccccccccc</td>
                <td>ddddddddddd</td>
            </tr>
            <tr>
                <td>aaaaaaaaaaa</td>
                <td>bbbbbbbbbbb</td>
                <td>ccccccccccc</td>
                <td>ddddddddddd</td>
            </tr>
            <tr>
                <td>aaaaaaaaaaa</td>
                <td>bbbbbbbbbbb</td>
                <td>ccccccccccc</td>
                <td>ddddddddddd</td>
            </tr>
        </tbody>
    </table>
<p id="demo" style="background-color:yellow">testest</p>
</body>
<script> 
window.onload = function(){
 document.addEventListener("scroll", myFunction);
 var i = 0;
 function myFunction() {
   document.getElementById("demo").innerHTML = "You scrolled in div." + i++;
  var lastScroll = document.getScroll();
   if(lastScroll[1] >= 100){
    document.getElementById("myDIV").classList.add('scroll');
   } else {
    document.getElementById("myDIV").classList.remove('scroll');
   }
 }
 document.getScroll = function() {
  if (window.pageYOffset != undefined) {
   return [pageXOffset, pageYOffset];
  } else {
  var sx, sy, d = document,
   r = d.documentElement,
   b = d.body;
   sx = r.scrollLeft || b.scrollLeft || 0;
   sy = r.scrollTop || b.scrollTop || 0;
  return [sx, sy];
  }
window.onload = function() {
  document.addEventListener("scroll", myFunction);
  var i = 0;
  function myFunction() {
    document.getElementById("demo").innerHTML = "You scrolled in div." + i++;
    var lastScroll = document.getScroll();
    if (lastScroll[1] >= 100) {
      document.getElementById("myDIV").classList.add('scroll');
    } else {
      document.getElementById("myDIV").classList.remove('scroll');
    }
  }
  document.getScroll = function() {
    if (window.pageYOffset != undefined) {
      return [pageXOffset, pageYOffset];
    } else {
      var sx, sy, d = document,
        r = d.documentElement,
        b = d.body;
      sx = r.scrollLeft || b.scrollLeft || 0;
      sy = r.scrollTop || b.scrollTop || 0;
      return [sx, sy];
    }
  }
}.scroll {
  position: fixed;
  top: 0 !important;
}
#myDIV {
  background-color: #ccc;
}
header {
  height: 100px;
}
footer {
  height: 2000px;
}<html>
<header>
</header>
<body>
  <table style="width:1900px">
    <thead id="myDIV">
      <tr>
        <th style="width:25%">Column1</th>
        <th style="width:25%">Column2</th>
        <th style="width:25%">Column3</th>
        <th style="width:25%">Column4</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td style="width:25%">aaaaaaaaaaa</td>
        <td style="width:25%">bbbbbbbbbbb</td>
        <td style="width:25%">ccccccccccc</td>
        <td style="width:25%">ddddddddddd</td>
      </tr>
      <tr>
        <td>aaaaaaaaaaa</td>
        <td>bbbbbbbbbbb</td>
        <td>ccccccccccc</td>
        <td>ddddddddddd</td>
      </tr>
      <tr>
        <td>aaaaaaaaaaa</td>
        <td>bbbbbbbbbbb</td>
        <td>ccccccccccc</td>
        <td>ddddddddddd</td>
      </tr>
      <tr>
        <td>aaaaaaaaaaa</td>
        <td>bbbbbbbbbbb</td>
        <td>ccccccccccc</td>
        <td>ddddddddddd</td>
      </tr>
      <tr>
        <td>aaaaaaaaaaa</td>
        <td>bbbbbbbbbbb</td>
        <td>ccccccccccc</td>
        <td>ddddddddddd</td>
      </tr>
      <tr>
        <td>aaaaaaaaaaa</td>
        <td>bbbbbbbbbbb</td>
        <td>ccccccccccc</td>
        <td>ddddddddddd</td>
      </tr>
      <tr>
        <td>aaaaaaaaaaa</td>
        <td>bbbbbbbbbbb</td>
        <td>ccccccccccc</td>
        <td>ddddddddddd</td>
      </tr>
    </tbody>
  </table>
  <p id="demo" style="background-color:yellow">testest</p>
</body>
<footer></footer> 
     
     
    