/* ============================================
   BOUTON SCROLL-TO-TOP
============================================ */
#scroll-top-btn {
    position: fixed;
    bottom: calc(var(--nav-height) + env(safe-area-inset-bottom, 0px) + 12px);
    right: 16px;
    width: 42px;
    height: 42px;
    border-radius: 50%;
    background: var(--primary);
    color: white;
    border: none;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1rem;
    box-shadow: 0 4px 16px rgba(0, 102, 204, 0.35);
    z-index: 8999;
    /* Caché par défaut */
    opacity: 0;
    pointer-events: none;
    transform: translateY(12px) scale(0.85);
    transition: opacity 0.3s ease, transform 0.3s ease;
}

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

#scroll-top-btn:active {
    transform: scale(0.92);
}

@media (min-width: 768px) {
    #scroll-top-btn {
        position: absolute; /* dans le container sur desktop */
        bottom: calc(var(--nav-height) + 12px);
    }
}