JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="ru">
<head>
</head>
<body>
    <canvas class="canvas" width="400" height="200"></canvas>
</body>
</html>

CSS

.canvas {
  border: 3px solid black;
}

JavaScript

let canvas = document.querySelector(".canvas");
let ctx = canvas.getContext("2d");

canvas.addEventListener("mousemove", function(event) {
  let mouseX = event.offsetX;
  let mouseY = event.offsetY;
  ctx.fillStyle = "rgb(250, 150," + mouseY + ");";
  ctx.fill();
  ctx.rect(mouseX, mouseY, 5, 5);
});