JSFiddle - React, Tailwind, and code Playground
HTML
<canvas width="101" height="101"></canvas>
CSS
canvas {
outline: 2px solid green;
}
JavaScript
var cvs = document.querySelector('canvas'),
ctx = cvs.getContext('2d');
var cx = cvs.width/2 | 0,
cy = cvs.height/2 | 0;
ctx.rect(cx-10, cy-10, 20, 20);
ctx.stroke();