JSFiddle - React, Tailwind, and code Playground

JavaScript

var ctx = document.body.appendChild(
    document.createElement('canvas')).getContext('2d');

ctx.moveTo(0, 0);
ctx.lineTo(20, 0);
ctx.lineTo(20, 20);
ctx.lineTo(0, 20);
ctx.lineTo(0, 0);

ctx.moveTo(5, 5);
ctx.lineTo(5, 15);
ctx.lineTo(15, 15);
ctx.lineTo(15, 5);
ctx.lineTo(5, 5);

ctx.fill();