make an interactive Iframe. A small red dot follows the mouse cursor when I'm on the iframe.

function move(event) {
    var dot = document.getElementById("dot");
    var x = event.clientX;
    var y = event.clientY;
    x -= x % 10;
    y -= y % 10;
    dot.style.left = x + "px";
    dot.style.top = y + "px";
}