JSFiddle - React, Tailwind, and code Playground

HTML

<canvas id='canvas' width="800" height="600" style="border:1px solid #000000;">Обновите браузер</canvas>

CSS

#canvas { background-color: rgba(158, 167, 184, 0.2); }

JavaScript

var canvas = document.getElementById("canvas"),
	ctx = canvas.getContext('2d'),
  side = 0,
  up  = 0;

 function drawRect () {
	ctx.fillStyle = "green";
	//ctx.clearRect(0, 0, 800, 600);
	ctx.fillRect (up, side, 25, 25);
}

drawRect ()