JSFiddle - React, Tailwind, and code Playground

HTML

<canvas id="okno">
  
</canvas>

JavaScript

var okno = document.getElementById("okno")
var ctx = okno.getContext('2d');

ctx.font = "20px Arial";

var cel = {};
cel.x = 10;
cel.y = 10;
cel.dlug = 25;
cel.szer = 25;
cel.xspeed = 55;
cel.yspeed = 2;

function clear (){
ctx.clearRect(0,0,900,600);
}

function draw (){
clear ();
ctx.fillRect(cel.x,cel.y,cel.dlug,cel.szer);
cel.x += cel.xspeed;
}

setInterval(draw, 300);