document.addEventListener('DOMContentLoaded', function() {
    const backToTop = document.querySelector('.back-to-top');

    backToTop.addEventListener('click', function() {
        window.scrollTo({
            top: 0,
            behavior: 'smooth'
        });
    });

    backToTop.addEventListener('mouseover', function() {
        const tooltip = this.querySelector('.tooltip');
        tooltip.style.opacity = '1';
        tooltip.style.transition = 'opacity 0.3s ease';  // 淡入时间为 0.3 秒
    });

    backToTop.addEventListener('mouseout', function() {
        const tooltip = this.querySelector('.tooltip');
        tooltip.style.opacity = '0';
        tooltip.style.transition = 'opacity 0.3s ease';  // 淡出时间为 0.3 秒
    });
});