实现弹力球效果，碰到屏幕边框弹回，效果如下

代码如下：

<img src="../image/ball.png" alt="" class="ball">
<style>
    .ball {
        position: fixed;
        top: 50vh;
        left: 50vw;
        width: 15vw;
        height: 15vw;
        border-radius: 50%;
        z-index: 0;
    }
</style>
<script src="https://code.jquery.com/jquery-3.7.1.js"></script>
<script>
    const ball = document.querySelector('.ball');
    let posX = window.innerWidth / 2;
    let posY = window.innerHeight / 2;
    let velX = 2;
    let velY = 2;
    const friction = 0.5;
    let rotation = 0;
    const rotationSpeed = 3;

    function moveBall() {
        posX += velX;
        posY += velY;

        // Bounce off the edges
        if (posX <= 0 || posX + ball.offsetWidth >= window.innerWidth) {
            velX = -velX * friction;
            posX = Math.min(Math.max(posX, 0), window.innerWidth - ball.offsetWidth);
        }

        if (posY <= 0 || posY + ball.offsetHeight >= window.innerHeight) {
            velY = -velY * friction;
            posY = Math.min(Math.max(posY, 0), window.innerHeight - ball.offsetHeight);
        }

        rotation += rotationSpeed;
        ball.style.left = posX + 'px';
        ball.style.top = posY + 'px';
        ball.style.transform = 'rotate(' + rotation + 'deg)';

        requestAnimationFrame(moveBall);
    }

    moveBall();
</script>