position html canvas relative to viewport

Hi,

I want to draw on a html canvas:

const topCanvas = document.createElement("canvas");

document.body.appendChild(topCanvas);

But the canvas is always positioned on the window and i can't find a way to position it relative to the viewport or layout:

topCanvas.style.position = "absolute";

topCanvas.style.left = "10px";

topCanvas.style.top = "10px";

topCanvas.style.width = "500px";

topCanvas.style.height = "500px";

thanks!