/* =========================================================
   BOTÓN VOLVER ARRIBA
   ========================================================= */
.top-btn {
    position: fixed;
    bottom: calc(88px + env(safe-area-inset-bottom));
    right: clamp(16px, 3vw, 38px);
    width: 50px;
    height: 50px;
    border-radius: 50%;
    background: var(--accent);
    color: var(--bg);
    border: none;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 10px 30px rgba(0,0,0,0.5);
    opacity: 0;
    transform: translateY(20px);
    pointer-events: none;
    transition: opacity 0.4s var(--ease-out), transform 0.4s var(--ease-out), background 0.3s;
    z-index: 100;
}

.top-btn svg { width: 20px; height: 20px; }

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

.top-btn:hover {
    background: var(--fg);
    transform: translateY(-3px);
}