.falling {
    position: fixed;
    top: -20px;
    font-size: 24px;
    color: red;
    pointer-events: none;
    animation: fall linear forwards;
    white-space: nowrap;  /* 防止换行 */
}

@keyframes fall {
    to {
        transform: translateY(100vh);
        opacity: 0;
    }
}