W3Schools Tryit Editor

<!DOCTYPE HTML>
<html>
<head>
<style>
.droptarget {
  width: 100px; 
  height: 35px;
  margin-right: 100px;
  padding: 10px;
  border: 1px solid black;
}
</style>
</head>
<body>
<h1>HTML DOM Events</h1>
<h2>The ondragenter Event</h2>

<p>Use the HTML DOM to assign "ondragstart", "ondragenter", "ondragleave", "ondragover" and "ondrop" events to the document object.</p>

<p>Drag the text up and down between the two rectangles:</p>

/* Events fired on the drop target */
document.ondragenter = function(event) {
  if ( event.target.className == "droptarget" ) {
    document.getElementById("demo").innerHTML = "Entered the dropzone";
    event.target.style.backgroundColor = "lightblue";
  }
};

document.ondragover = function(event) {
  event.preventDefault();
};

document.ondragleave = function(event) {
  if (event.target.className == "droptarget") {
    document.getElementById("demo").innerHTML = "Left the dropzone";
    event.target.style.backgroundColor = "";
  }
};

document.ondrop = function(event) {
  event.preventDefault();
  if (event.target.className == "droptarget") {
    event.target.style.backgroundColor = "";
    const data = event.dataTransfer.getData("Text");
    event.target.appendChild(document.getElementById(data));
  }
};
</script>

</body>
</html>