.back-to-top {
    position: fixed;
    right: max(18px, env(safe-area-inset-right));
    bottom: max(18px, env(safe-area-inset-bottom));
    z-index: 1100;
    display: grid;
    width: 44px;
    height: 44px;
    padding: 0;
    place-items: center;
    color: var(--button-text, #333);
    background: var(--button-bg, #ffcd00);
    border: 1px solid var(--button-border, #cc9a00);
    border-radius: var(--radius-full, 9999px);
    box-shadow: var(--shadow-md, 0 10px 25px rgba(15, 23, 42, 0.22));
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px) scale(0.92);
    transition:
        opacity var(--motion-normal, 200ms) var(--motion-ease, ease),
        transform var(--motion-normal, 200ms) var(--motion-ease, ease),
        visibility var(--motion-normal, 200ms);
}

.back-to-top.is-visible {
    opacity: 0.88;
    visibility: visible;
    transform: translateY(0) scale(1);
}

.back-to-top:hover {
    opacity: 1;
    transform: translateY(-2px) scale(1.04);
    box-shadow: var(--shadow-lg, 0 18px 40px rgba(15, 23, 42, 0.28));
}

.back-to-top:focus-visible {
    opacity: 1;
    outline: var(--focus-ring-width, 3px) solid var(--focus-ring-color-primary, rgba(255, 205, 0, 0.5));
    outline-offset: 3px;
}

.back-to-top__icon {
    width: 21px;
    height: 21px;
    pointer-events: none;
}

.back-to-top__tooltip {
    position: absolute;
    right: calc(100% + 10px);
    padding: 6px 9px;
    color: var(--text-primary, #ededed);
    font: 500 0.78rem/1 var(--font-family-ui, "Inter", system-ui, sans-serif);
    white-space: nowrap;
    background: var(--bg-tertiary, #3d3d3d);
    border: 1px solid var(--medium-border-color, #444);
    border-radius: var(--radius-md, 6px);
    box-shadow: var(--shadow-sm, 0 2px 4px rgba(15, 23, 42, 0.22));
    opacity: 0;
    visibility: hidden;
    transform: translateX(4px);
    transition:
        opacity var(--motion-fast, 150ms) var(--motion-ease, ease),
        transform var(--motion-fast, 150ms) var(--motion-ease, ease),
        visibility var(--motion-fast, 150ms);
}

.back-to-top:hover .back-to-top__tooltip,
.back-to-top:focus-visible .back-to-top__tooltip {
    opacity: 1;
    visibility: visible;
    transform: translateX(0);
}

@media (max-width: 600px) {
    .back-to-top {
        right: max(12px, env(safe-area-inset-right));
        bottom: max(12px, env(safe-area-inset-bottom));
        width: 40px;
        height: 40px;
    }

    .back-to-top__tooltip {
        display: none;
    }
}

@media (prefers-reduced-motion: reduce) {
    .back-to-top,
    .back-to-top__tooltip {
        transition-duration: 0.01ms;
    }
}