<DOOCTYPE html>
<meta charset = "UTF-8">
<html>
<body style = "margin: 0;">
<style>
</style>
<canvas id = "canvas"></canvas>
<script>
var
canv = document.getElementById("canvas");
ctx = canv.getContext('2d')
canv.width = window.innerWidth;
canv.height = window.innerHeight;
canv.fillRect(0, 0, 10, 10);
</script>
</body>
</html>