/* 向上箭头按钮容器 */
#backToTop {
    position: fixed;
    bottom: 40px;
    right: 25px;
    width: 60px;
    height: 60px;
    background: rgba(0, 0, 0, 0.4); /* 半透明毛玻璃底 */
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    opacity: 0; /* 默认隐藏 */
    transform: scale(0.8);
    transition: opacity 0.4s ease, transform 0.3s ease;
    z-index: 999;
    backdrop-filter: blur(6px); /* 毛玻璃效果 */
    box-shadow: 0 0 12px rgba(255, 165, 0, 0.4); /* 初始橙色微光 */
}

/* 悬浮状态放大+更亮光效 */
#backToTop:hover {
    transform: scale(1);
    box-shadow: 0 0 25px rgba(255, 215, 0, 0.9); /* 金色光晕 */
}

/* SVG箭头路径渐变发光 */
.arrow-svg path {
    stroke: url(#arrow-gradient);
    filter: drop-shadow(0 0 6px #FFA500) drop-shadow(0 0 15px #FFD700);
    animation: glow 2s infinite alternate;
}

/* 发光动画：橙色到金色渐变呼吸 */
@keyframes glow {
    0% {
        filter: drop-shadow(0 0 5px #FFA500) drop-shadow(0 0 15px #FFA500);
    }
    100% {
        filter: drop-shadow(0 0 10px #FFD700) drop-shadow(0 0 30px #FFD700);
    }
}