/*
 * MT-Bike Flipbook
 * Cover und Rückseite werden groß als Einzelseite angezeigt.
 * Beim ersten Umblättern öffnet sich der sichtbare Bereich zur Doppelseite.
 */

.flipbook-section {
    margin-top: 4.5rem;
}

.flipbook-intro {
    max-width: 780px;
    margin-bottom: 1.75rem;
}

.flipbook-shell {
    position: relative;
    overflow: hidden;
    padding: clamp(0.85rem, 2.5vw, 2rem);
    border: 1px solid rgba(255, 255, 255, 0.14);
    border-radius: 28px;
    background:
        radial-gradient(circle at 50% 0%, rgba(255, 255, 255, 0.16), transparent 42%),
        linear-gradient(145deg, rgba(24, 29, 34, 0.98), rgba(9, 12, 15, 0.98));
    box-shadow: 0 32px 90px rgba(0, 0, 0, 0.28);
}

.flipbook-stage {
    position: relative;
    display: grid;
    place-items: center;
    min-height: clamp(520px, 70vw, 860px);
    padding: clamp(0.35rem, 1.8vw, 1.35rem);
    overflow: auto;
    border-radius: 20px;
    background:
        radial-gradient(ellipse at center, rgba(255,255,255,0.085), transparent 66%),
        linear-gradient(145deg, rgba(255,255,255,0.025), rgba(0,0,0,0.08));
    isolation: isolate;
}

.flipbook-stage::after {
    content: "";
    position: absolute;
    left: 12%;
    right: 12%;
    bottom: 3%;
    height: 8%;
    border-radius: 50%;
    background: rgba(0,0,0,0.38);
    filter: blur(22px);
    z-index: -1;
}

/*
 * Dieser Viewport schneidet beim Cover die unsichtbare zweite Buchhälfte ab.
 * Seine Breite wächst beim Öffnen weich von einer auf zwei Seiten.
 */
.flipbook-book-viewport {
    position: relative;
    overflow: hidden;
    flex: 0 0 auto;
    max-width: none;
    max-height: none;
    transition:
        width 380ms cubic-bezier(.22,.72,.22,1),
        height 380ms cubic-bezier(.22,.72,.22,1);
    will-change: width, height;
}

.flipbook-book-viewport.no-transition {
    transition: none !important;
}

.flipbook-zoom-layer {
    position: absolute;
    top: 0;
    transform-origin: top left;
    transition:
        left 380ms cubic-bezier(.22,.72,.22,1),
        transform 280ms cubic-bezier(.2,.75,.25,1);
    will-change: left, transform;
}

#mtbikeBook {
    width: 1400px;
    height: 700px;
    opacity: 0;
    transform: translateY(14px) scale(0.985);
    transition: opacity 420ms ease, transform 620ms cubic-bezier(.2,.8,.2,1);
}

.flipbook-shell.is-ready #mtbikeBook {
    opacity: 1;
    transform: none;
}

/* Keine CSS-Fläche außerhalb echter Seiten. */
.stf__parent,
.stf__block,
.stf__item,
.stf__parent canvas,
.stf__item canvas {
    background: transparent !important;
}

.flipbook-loader {
    position: absolute;
    inset: 0;
    z-index: 20;
    display: grid;
    place-content: center;
    gap: 0.9rem;
    text-align: center;
    color: #fff;
    background: rgba(9, 12, 15, 0.94);
    transition: opacity 320ms ease, visibility 320ms ease;
}

.flipbook-shell.is-ready .flipbook-loader {
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
}

.flipbook-loader-spinner {
    width: 42px;
    height: 42px;
    margin: 0 auto;
    border: 3px solid rgba(255,255,255,0.2);
    border-top-color: #fff;
    border-radius: 50%;
    animation: flipbookSpin 0.85s linear infinite;
}

@keyframes flipbookSpin {
    to { transform: rotate(360deg); }
}

.flipbook-toolbar {
    display: grid;
    grid-template-columns: auto 1fr auto;
    align-items: center;
    gap: 1rem;
    margin-top: 1.25rem;
}

.flipbook-nav,
.flipbook-actions {
    display: flex;
    align-items: center;
    gap: 0.6rem;
}

.flipbook-actions {
    justify-self: end;
}

.flipbook-button {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 46px;
    height: 46px;
    padding: 0 1rem;
    border: 1px solid rgba(255,255,255,0.22);
    border-radius: 999px;
    color: #fff;
    background: rgba(255,255,255,0.08);
    font: inherit;
    line-height: 1;
    cursor: pointer;
    text-decoration: none;
    transition: background 180ms ease, transform 180ms ease, opacity 180ms ease;
}

.flipbook-button:hover:not(:disabled) {
    background: rgba(255,255,255,0.16);
    transform: translateY(-1px);
}

.flipbook-button:disabled {
    opacity: 0.35;
    cursor: default;
}

.flipbook-page-status {
    justify-self: center;
    color: rgba(255,255,255,0.88);
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.03em;
}

.flipbook-hint {
    margin: 0.9rem 0 0;
    color: rgba(255,255,255,0.55);
    text-align: center;
    font-size: 0.92rem;
}

.flipbook-shell:fullscreen {
    display: grid;
    grid-template-rows: 1fr auto auto;
    border-radius: 0;
    padding: 1rem;
}

.flipbook-shell:fullscreen .flipbook-stage {
    min-height: 0;
}

@media (max-width: 820px) {
    .flipbook-stage {
        min-height: clamp(450px, 112vw, 760px);
    }

    .flipbook-toolbar {
        grid-template-columns: 1fr auto;
    }

    .flipbook-page-status {
        grid-column: 1 / -1;
        grid-row: 1;
    }

    .flipbook-nav {
        grid-column: 1;
        grid-row: 2;
    }

    .flipbook-actions {
        grid-column: 2;
        grid-row: 2;
    }

    .flipbook-open-pdf {
        padding-inline: 0.85rem;
    }
}

@media (max-width: 520px) {
    .flipbook-shell {
        border-radius: 20px;
        padding: 0.65rem;
    }

    .flipbook-button {
        min-width: 42px;
        height: 42px;
        padding-inline: 0.75rem;
    }

    .flipbook-open-pdf {
        font-size: 0.86rem;
    }
}

@media (prefers-reduced-motion: reduce) {
    #mtbikeBook,
    .flipbook-loader,
    .flipbook-book-viewport,
    .flipbook-zoom-layer {
        transition: none;
    }

    .flipbook-loader-spinner {
        animation: none;
    }
}