.scroll-top-btn {
    position: fixed;
    bottom: 32px;
    right: 28px;
    z-index: 900;
    width: 44px;
    height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: var(--color-bg-elevated);
    border: 1.5px solid var(--color-border-base);
    border-radius: var(--radius-sm);
    color: var(--color-text-secondary);
    font-size: 16px;
    cursor: pointer;
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--transition-base), visibility var(--transition-base), border-color var(--transition-base), box-shadow var(--transition-base), color var(--transition-base);
    pointer-events: none;
}

.scroll-top-btn.is-visible {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
}

.scroll-top-btn:hover {
    border-color: var(--color-primary);
    box-shadow: 0 0 18px var(--color-primary-glow);
    color: var(--color-text-primary);
}

@media (max-width: 480px) {
    .scroll-top-btn {
        bottom: 20px;
        right: 16px;
        width: 40px;
        height: 40px;
        font-size: 14px;
    }
}