/* ════════════════════════════════════════
   SECTION 1 — FLIP GALLERY
════════════════════════════════════════ */
.bi-gallery {
    padding: 90px 80px;
    background: #fff;
}

.bi-gallery__header {
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 12px;
    margin-bottom: 56px;
}

.bi-gallery__grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(2, 1fr);
    gap: 20px;
}

/* Flip card */
.bi-flip-card {
    height: 320px;
    perspective: 1000px;
    cursor: pointer;
}

.bi-flip-card__inner {
    position: relative;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
    transition: transform 0.65s cubic-bezier(0.4, 0.2, 0.2, 1);
}

.bi-flip-card:hover .bi-flip-card__inner {
    transform: rotateY(180deg);
}

.bi-flip-card__front,
.bi-flip-card__back {
    position: absolute;
    inset: 0;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    overflow: hidden;
}

.bi-flip-card__front img,
.bi-flip-card__back img {
    width: 100%;
    height: 100%;
    object-fit: contain;
    background: #f4f8ff;
    display: block;
    transition: transform 0.4s ease;
}

.bi-flip-card:hover .bi-flip-card__front img {
    transform: scale(1.04);
}

.bi-flip-card__back {
    transform: rotateY(180deg);
}

.bi-flip-card__overlay {
    position: absolute;
    top: 10px;
    left: 10px;
    background: #0093ff;
    padding: 5px 12px;
    display: flex;
    align-items: center;
    gap: 6px;
    color: #fff;
}

.bi-flip-card__overlay span {
    font-family: 'TTFirsNeue', sans-serif;
    font-weight: 700;
    font-size: 11px;
    letter-spacing: 1px;
    text-transform: uppercase;
}

/* ════════════════════════════════════════
   SECTION 2 — WHY BOOK COVER MATTERS
════════════════════════════════════════ */
.bi-why {
    padding: 90px 80px;
    background: #0d1b2a;
    background-image:
        linear-gradient(rgba(0,147,255,0.07) 1px, transparent 1px),
        linear-gradient(90deg, rgba(0,147,255,0.07) 1px, transparent 1px);
    background-size: 60px 60px;
}

.bi-why__header {
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 12px;
    margin-bottom: 56px;
}

.bi-why__header .section-title,
.bi-why__header .section-text {
    color: #fff;
}

.bi-why__header .section-text {
    color: rgba(255,255,255,0.6);
}

.bi-why__grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
    margin-bottom: 60px;
}

.bi-why__card {
    background: rgba(255,255,255,0.04);
    border: 1px solid rgba(255,255,255,0.07);
    padding: 36px 28px;
    display: flex;
    flex-direction: column;
    gap: 14px;
    transition: background 0.3s ease, border-color 0.3s ease, transform 0.3s ease;
}

.bi-why__card:hover {
    background: rgba(0,147,255,0.1);
    border-color: #0093ff;
    transform: translateY(-6px);
}

.bi-why__card-icon {
    width: 58px;
    height: 58px;
    background: rgba(0,147,255,0.12);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 26px;
    color: #0093ff;
    transition: background 0.3s ease, color 0.3s ease;
}

.bi-why__card:hover .bi-why__card-icon {
    background: #0093ff;
    color: #fff;
}

.bi-why__card h4 {
    font-family: 'TTFirsNeue', sans-serif;
    font-weight: 700;
    font-size: 17px;
    color: #fff;
    margin: 0;
}

.bi-why__card p {
    font-family: 'nexa', sans-serif;
    font-size: 14px;
    line-height: 1.75;
    color: rgba(255,255,255,0.6);
    margin: 0;
}

/* Stat bar */
.bi-why__stat-bar {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0;
    background: rgba(0,147,255,0.1);
    border: 1px solid rgba(0,147,255,0.2);
    padding: 36px 40px;
}

.bi-why__stat {
    flex: 1;
    text-align: center;
}

.bi-why__stat span {
    font-family: 'TTFirsNeue', sans-serif;
    font-weight: 800;
    font-size: 42px;
    color: #0093ff;
    display: block;
    line-height: 1;
}

.bi-why__stat p {
    font-family: 'nexa', sans-serif;
    font-size: 13px;
    color: rgba(255,255,255,0.6);
    margin: 8px 0 0;
}

.bi-why__stat-divider {
    width: 1px;
    height: 60px;
    background: rgba(255,255,255,0.1);
    flex-shrink: 0;
    margin: 0 20px;
}

/* ════════════════════════════════════════
   SECTION 3 — WHY CHOOSE US
════════════════════════════════════════ */
.bi-choose {
    display: flex;
    align-items: center;
    gap: 80px;
    padding: 90px 80px;
    background: #f4f8ff;
    background-image:
        linear-gradient(rgba(0,147,255,0.05) 1px, transparent 1px),
        linear-gradient(90deg, rgba(0,147,255,0.05) 1px, transparent 1px);
    background-size: 60px 60px;
}

.bi-choose__left {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.bi-choose__items {
    display: flex;
    flex-direction: column;
    gap: 18px;
    margin-top: 8px;
}

.bi-choose__item {
    display: flex;
    align-items: flex-start;
    gap: 14px;
}

.bi-choose__item-icon {
    font-size: 24px;
    color: #0093ff;
    flex-shrink: 0;
    margin-top: 2px;
}

.bi-choose__item h4 {
    font-family: 'TTFirsNeue', sans-serif;
    font-weight: 700;
    font-size: 15px;
    color: #0d1b2a;
    margin: 0 0 4px;
}

.bi-choose__item p {
    font-family: 'nexa', sans-serif;
    font-size: 13px;
    color: #5a6a82;
    line-height: 1.7;
    margin: 0;
}

/* Right — stacked books visual */
.bi-choose__right {
    flex: 0 0 420px;
    position: relative;
    height: 480px;
}

.bi-choose__books {
    position: relative;
    width: 100%;
    height: 100%;
}

.bi-choose__book {
    position: absolute;
    overflow: hidden;
    box-shadow: 0 16px 48px rgba(0,0,0,0.14);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.bi-choose__book img {
    width: 100%;
    height: 100%;
    object-fit: contain;
    background: #eef3fb;
    display: block;
}

.bi-choose__book--1 {
    width: 220px;
    height: 300px;
    top: 0;
    left: 0;
    z-index: 3;
}

.bi-choose__book--2 {
    width: 200px;
    height: 280px;
    top: 60px;
    left: 130px;
    z-index: 2;
    opacity: 0.92;
}

.bi-choose__book--3 {
    width: 180px;
    height: 260px;
    top: 130px;
    left: 240px;
    z-index: 1;
    opacity: 0.8;
}

.bi-choose__book:hover {
    transform: translateY(-8px) scale(1.03);
    box-shadow: 0 24px 60px rgba(0,147,255,0.2);
    z-index: 10;
    opacity: 1;
}

.bi-choose__badge {
    position: absolute;
    bottom: 20px;
    right: 0;
    background: #0093ff;
    color: #fff;
    padding: 16px 22px;
    display: flex;
    align-items: center;
    gap: 10px;
    font-family: 'TTFirsNeue', sans-serif;
    font-weight: 700;
    font-size: 14px;
    box-shadow: 0 8px 24px rgba(0,147,255,0.4);
    z-index: 11;
}

.bi-choose__badge i {
    font-size: 22px;
}

/* ════════════════════════════════════════
   RESPONSIVE
════════════════════════════════════════ */
@media (max-width: 1200px) {
    .bi-gallery__grid {
        grid-template-columns: repeat(4, 1fr);
    }
}

@media (max-width: 1024px) {
    .bi-gallery,
    .bi-why,
    .bi-choose {
        padding-left: 40px;
        padding-right: 40px;
    }

    .bi-choose {
        flex-direction: column;
    }

    .bi-choose__right {
        flex: none;
        width: 100%;
        height: 360px;
    }

    .bi-why__grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .bi-why__stat-bar {
        flex-wrap: wrap;
        gap: 24px;
        padding: 28px 24px;
    }

    .bi-why__stat-divider { display: none; }
}

@media (max-width: 768px) {
    .bi-gallery,
    .bi-why,
    .bi-choose {
        padding-left: 20px;
        padding-right: 20px;
    }

    .bi-gallery__grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .bi-flip-card { height: 240px; }

    .bi-why__grid {
        grid-template-columns: 1fr;
    }

    .bi-choose__right {
        height: 300px;
    }

    .bi-choose__book--1 { width: 170px; height: 240px; }
    .bi-choose__book--2 { width: 155px; height: 220px; left: 100px; }
    .bi-choose__book--3 { width: 140px; height: 200px; left: 190px; }
}

@media (max-width: 480px) {
    .bi-gallery__grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 12px;
    }

    .bi-flip-card { height: 200px; }
}