/**
 * Кнопка «Наверх» — warm corporate, с прогресс-кольцом прокрутки
 */

.site-scroll-top {
    --scroll-progress: 0;
    position: fixed;
    right: 24px;
    bottom: 24px;
    width: 52px;
    height: 52px;
    padding: 0;
    border: none;
    border-radius: 50%;
    background: transparent;
    cursor: pointer;
    z-index: 10000;
    opacity: 0;
    visibility: hidden;
    transform: translateY(20px) scale(0.85);
    transition:
        opacity 0.4s ease,
        visibility 0.4s ease,
        transform 0.45s cubic-bezier(0.34, 1.4, 0.64, 1);
    overflow: visible;
}

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

.site-scroll-top:hover {
    transform: translateY(-2px) scale(1.06);
}

.site-scroll-top.is-visible:hover {
    transform: translateY(-2px) scale(1.06);
}

.site-scroll-top:active {
    transform: translateY(0) scale(0.96);
    transition-duration: 0.12s;
}

.site-scroll-top:focus {
    outline: none;
}

.site-scroll-top:focus-visible .site-scroll-top__inner {
    box-shadow:
        0 4px 20px rgba(var(--color-accent-rgb), 0.35),
        0 0 0 3px rgba(var(--color-accent-rgb), 0.35);
}

/* Прогресс-кольцо */
.site-scroll-top__ring {
    position: absolute;
    inset: 0;
    border-radius: 50%;
    background: conic-gradient(
        var(--color-accent) calc(var(--scroll-progress) * 360deg),
        rgba(var(--color-accent-rgb), 0.18) 0
    );
    box-shadow: 0 4px 20px rgba(var(--color-accent-rgb), 0.25);
    transition: box-shadow 0.25s ease;
    pointer-events: none;
}

.site-scroll-top:hover .site-scroll-top__ring {
    box-shadow: 0 6px 28px rgba(var(--color-accent-rgb), 0.45);
}

/* Внутренняя кнопка */
.site-scroll-top__inner {
    position: absolute;
    inset: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 50%;
    background: var(--gradient-accent);
    color: var(--color-text-on-accent);
    font-size: 18px;
    line-height: 1;
    transition: transform 0.3s cubic-bezier(0.34, 1.4, 0.64, 1);
}

.site-scroll-top:hover .site-scroll-top__inner {
    transform: translateY(-1px);
}

.site-scroll-top.is-scrolling .site-scroll-top__inner {
    animation: site-scroll-top-bounce 0.6s ease;
}

@keyframes site-scroll-top-bounce {
    0%, 100% { transform: translateY(0); }
    40% { transform: translateY(-5px); }
    70% { transform: translateY(2px); }
}

@media (max-width: 767px) {
    .site-scroll-top {
        right: 16px;
        bottom: 16px;
        width: 46px;
        height: 46px;
    }

    .site-scroll-top__inner {
        font-size: 16px;
    }
}

@media (prefers-reduced-motion: reduce) {
    .site-scroll-top,
    .site-scroll-top__inner {
        transition: none;
        animation: none;
    }

    .site-scroll-top.is-scrolling .site-scroll-top__inner {
        animation: none;
    }
}