JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <head>
    <style type="text/css">
      html,body{
        width:100%;
        height:100%;
      }
    </style>
        <script>
        document.addEventListener("DOMContentLoaded", function() {

var player = document.createElement('div');
player.style.position = 'absolute';
player.style.width = '20px';
player.style.height = '20px';
player.style.backgroundColor = 'red';
player.style.bottom = '10px';
player.style.left = '10px';
document.body.appendChild(player);

player.style.borderRadius = '50%';

var playerX = 10;
var playerY = 10;
var playerDirectionX = 5;
var playerDirectionY = 5;

function movePlayer() {
    playerX += playerDirectionX;
    playerY += playerDirectionY

  if (playerX > document.body.clientWidth - 20 || playerX < 0) {
    playerDirectionX = playerDirectionX * -1;
}
  if (playerY > document.body.clientHeight - 20 || playerY < 0){ 
playerDirectionY = playerDirectionY * -1;     
  }
  player.style.left = playerX + 'px';
  player.style.top = playerY + 'px';
}

setInterval(movePlayer, 50);

var playerDirection = document.createElement('div');
playerDirection.style.position = 'absolute';
playerDirection.style.width = '200px';
playerDirection.style.height = '20px';
playerDirection.style.top = '0px';
playerDirection.style.right = '0px';
document.body.appendChild(playerDirection);

function printPlayerDirection() {
  playerDirection.innerHTML = 'playerDirectionX: ' + playerDirectionX + ' playerDirectionY: ' + playerDirectionY + '<br/> score:' + score;
}

setInterval(printPlayerDirection, 50);

document.body.style.overflow = 'hidden';

document.onkeydown = function(e) {
  if (e.keyCode == 39) {
    playerDirectionX = playerDirectionX + 5; 
  }
else if (e.keyCode == 37) {
    playerDirectionX = playerDirectionX - 5; 
  }else if (e.keyCode == 38) {
    playerDirectionY = playerDirectionY - 5; 
  }
else if (e.keyCode == 40) {
    playerDirectionY = playerDirectionY + 5; 
  }else if (e.keyCode == 38) {
    playerDirectionY = playerDirectionY -...