/* === Ethereal Glass 滚动到顶部 === */
:root {
    --scroll-btn-size: 54px;
}

/* === 浮动岛屿按钮 === */
.scroll-top-btn {
    position: fixed;
    bottom: var(--space-8, 32px);
    right: var(--space-8, 32px);
    width: var(--scroll-btn-size);
    height: var(--scroll-btn-size);
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(255, 255, 255, 0.03);
    color: var(--color-text, rgba(255,255,255,0.85));
    border: 0.5px solid rgba(255, 255, 255, 0.06);
    border-radius: var(--radius-full, 9999px);
    cursor: pointer;
    opacity: 0;
    transform: translateY(20px) scale(0.85);
    transition: all 0.5s cubic-bezier(0.32, 0.72, 0, 1);
    z-index: 1000;
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    box-shadow: 0 4px 24px rgba(0, 0, 0, 0.3);
    padding: 0;
    outline: none;
    overflow: hidden;
}

.scroll-top-btn.visible {
    opacity: 1;
    transform: translateY(0) scale(1);
}

.scroll-top-btn:hover {
    border-color: rgba(106, 130, 251, 0.2);
    transform: translateY(-4px) scale(1.06);
    box-shadow: 0 8px 32px rgba(106, 130, 251, 0.12);
}

.scroll-top-btn:active {
    transform: translateY(0) scale(0.96);
}

.scroll-top-btn svg {
    width: 22px;
    height: 22px;
    stroke-width: 1.5;
    position: relative;
    z-index: 2;
    transition: transform 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.scroll-top-btn:hover svg {
    transform: translateY(-3px);
}

/* === 进度圆环 === */
.progress-circle {
    position: absolute;
    inset: 0;
    border-radius: var(--radius-full, 9999px);
    background: conic-gradient(rgba(106, 130, 251, 0.3) 0%, transparent 0%);
    z-index: 1;
    transition: background 0.1s cubic-bezier(0.32, 0.72, 0, 1);
    -webkit-mask: radial-gradient(transparent calc(50% - 3px), white calc(50% - 3px + 0.5px));
    mask: radial-gradient(transparent calc(50% - 3px), white calc(50% - 3px + 0.5px));
}

.progress-text {
    position: absolute;
    bottom: 10px;
    font-family: 'Space Grotesk', system-ui, sans-serif;
    font-size: 10px;
    font-weight: 500;
    color: var(--color-text-tertiary, rgba(255,255,255,0.35));
    z-index: 2;
    opacity: 0.6;
    transition: opacity 0.3s cubic-bezier(0.32, 0.72, 0, 1);
}

.scroll-top-btn:hover .progress-text {
    opacity: 1;
}

/* === 涟漪效果 === */
.scroll-top-btn::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 4px;
    height: 4px;
    background: rgba(106, 130, 251, 0.2);
    opacity: 0;
    border-radius: 50%;
    transform: translate(-50%, -50%);
}

.scroll-top-btn:focus:not(:active)::after {
    animation: ripple 0.6s ease-out;
}

@keyframes ripple {
    0% { transform: scale(0); opacity: 0.4; }
    100% { transform: scale(20); opacity: 0; }
}

/* === 响应式 === */
@media (max-width: 768px) {
    :root {
        --scroll-btn-size: 48px;
    }

    .scroll-top-btn {
        right: var(--space-6, 24px);
        bottom: var(--space-6, 24px);
    }

    .progress-text {
        display: none;
    }
}

@media (max-width: 480px) {
    .scroll-top-btn {
        width: 44px;
        height: 44px;
        right: 16px;
        bottom: 16px;
    }

    .scroll-top-btn svg {
        width: 18px;
        height: 18px;
    }
}