/* ── Back-to-top button ───────────────────────────────────── */
.btt-btn {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    z-index: 8990;
    width: 2.5rem;
    height: 2.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(112, 43, 220, 0.18);
    border: 0.0625rem solid rgba(124, 58, 237, 0.35);
    border-radius: 50%;
    color: rgba(255, 255, 255, 0.75);
    cursor: pointer;
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    opacity: 0;
    pointer-events: none;
    transform: translateY(0.5rem);
    transition: opacity 0.25s ease, transform 0.25s ease,
                background 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
}

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

.btt-btn:hover {
    background: rgba(124, 58, 237, 0.45);
    border-color: rgba(124, 58, 237, 0.7);
    color: #ffffff;
    box-shadow: 0 0 1rem rgba(124, 58, 237, 0.4);
}