You can edit / change the code and click run button <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>HTML5 canvas demo</title> <style>p {font-family: monospace;}</style> <script>var clicky_site_ids = clicky_site_ids || []; clicky_site_ids.push(101319977);</script><script async src="//static.getclicky.com/js"></script> <p>Canvas pane goes here:</p> <canvas id="pane" width="300" height="200"></canvas> <script> var canvas = document.getElementById('pane'); var context = canvas.getContext('2d'); context.fillStyle = 'rgb(250,0,0)'; context.fillRect(10, 10, 55, 50); context.fillStyle = 'rgba(0, 0, 250, 0.5)'; context.fillRect(30, 30, 55, 50); </script>