.portfolio-book {
    position: fixed;
    inset: var(--nav-height) 0 var(--booknav-height) 0;
    z-index: var(--z-stage);
    display: grid;
    place-items: center;
    perspective: 2500px;
    perspective-origin: 50% 45%;
}

.book {
    position: relative;
    width: calc(var(--page-w) * 2);
    height: var(--page-h);
    transform-style: preserve-3d;
    will-change: transform;
}

.book-page {
    position: absolute;
    top: 0;
    left: 50%;
    width: 50%;
    height: 100%;
    transform-origin: left center;
    transform-style: preserve-3d;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
}

.book-page.is-animating {
    will-change: transform;
}

.book-page:not(.is-current) {
    pointer-events: none;
}

.page-front,
.page-back {
    position: absolute;
    inset: 0;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    border: 1px solid var(--border);
    overflow: hidden;
}

.page-front {
    container-type: size;
    container-name: page;
    background:
        radial-gradient(120% 90% at 100% 0%, rgba(99, 102, 241, 0.07), transparent 55%),
        linear-gradient(180deg, rgba(255, 255, 255, 0.02), transparent 30%),
        var(--bg-secondary);
    border-radius: 6px var(--radius-lg) var(--radius-lg) 6px;
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.05), var(--shadow-soft);
    transform: translateZ(0.1px);
}

.page-front::before {
    content: "";
    position: absolute;
    inset: 0;
    border-radius: inherit;
    pointer-events: none;
    background: linear-gradient(90deg, rgba(0, 0, 0, 0.42), rgba(0, 0, 0, 0.08) 46px, transparent 110px);
}

.page-back {
    transform: rotateY(180deg) translateZ(0.1px);
    border-radius: var(--radius-lg) 6px 6px var(--radius-lg);
    background:
        radial-gradient(120% 90% at 0% 0%, rgba(34, 211, 238, 0.05), transparent 55%),
        linear-gradient(180deg, rgba(255, 255, 255, 0.015), transparent 30%),
        var(--bg-secondary);
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.04), var(--shadow-soft);
}

.page-back::before {
    content: "";
    position: absolute;
    inset: 0;
    border-radius: inherit;
    pointer-events: none;
    background: linear-gradient(-90deg, rgba(0, 0, 0, 0.42), rgba(0, 0, 0, 0.08) 46px, transparent 110px);
}

.page-back-inner {
    position: absolute;
    inset: 0;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    padding: clamp(20px, 4cqw, 40px);
}

.page-back-num {
    font-family: var(--font-display);
    font-size: clamp(90px, 16cqw, 170px);
    font-weight: 700;
    line-height: 0.9;
    color: transparent;
    -webkit-text-stroke: 1px rgba(148, 163, 184, 0.28);
}

.page-back-chapter {
    font-family: var(--font-display);
    font-size: 12px;
    font-weight: 600;
    letter-spacing: 0.42em;
    color: var(--text-muted);
    text-transform: uppercase;
    margin-top: 8px;
}

.page-back-lines {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.page-back-lines i {
    display: block;
    height: 1px;
    width: 46%;
    background: linear-gradient(90deg, rgba(148, 163, 184, 0.25), transparent);
}

.page-back-lines i:nth-child(2) { width: 62%; }
.page-back-lines i:nth-child(3) { width: 34%; }

.page-back-next,
.page-back-mark {
    font-size: 11px;
    letter-spacing: 0.32em;
    color: var(--text-muted);
    text-transform: uppercase;
}

.page-back-mark {
    font-family: var(--font-display);
    font-weight: 700;
    font-size: 14px;
    letter-spacing: 0.08em;
    color: var(--text-secondary);
}

.page-inner {
    position: relative;
    z-index: 2;
    height: 100%;
    display: flex;
    flex-direction: column;
}

.page-inner-cover {
    background:
        radial-gradient(90% 70% at 78% 22%, rgba(139, 92, 246, 0.14), transparent 60%),
        radial-gradient(70% 60% at 15% 85%, rgba(34, 211, 238, 0.08), transparent 60%);
}

.page-inner-backcover {
    background:
        radial-gradient(90% 70% at 50% 0%, rgba(99, 102, 241, 0.12), transparent 65%);
}

.page-content {
    flex: 1;
    overflow-y: auto;
    overflow-x: hidden;
    padding: clamp(20px, 4cqw, 42px) clamp(20px, 4.2cqw, 46px) 26px;
    overscroll-behavior: contain;
    -webkit-overflow-scrolling: touch;
}

.page-foot {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 12px;
    padding: 12px clamp(20px, 4.2cqw, 46px) 14px;
    border-top: 1px solid var(--border);
    font-size: 10.5px;
    letter-spacing: 0.28em;
    text-transform: uppercase;
    color: var(--text-muted);
    background: rgba(0, 0, 0, 0.16);
}

.page-number {
    display: inline-flex;
    align-items: baseline;
    gap: 5px;
    font-family: var(--font-display);
    letter-spacing: 0.12em;
    color: var(--text-secondary);
}

.page-number-current {
    font-size: 13px;
    font-weight: 700;
    color: var(--text-primary);
}

.page-number-sep {
    color: var(--text-muted);
}

.flip-shade,
.flip-glow {
    position: absolute;
    inset: 0;
    border-radius: inherit;
    pointer-events: none;
    opacity: 0;
    z-index: 5;
}

.flip-shade {
    background: linear-gradient(90deg, rgba(0, 0, 0, 0.85), rgba(0, 0, 0, 0.25) 45%, rgba(255, 255, 255, 0.06));
}

.flip-glow {
    background: linear-gradient(100deg, transparent 20%, rgba(255, 255, 255, 0.16) 48%, transparent 76%);
}

.book-spine {
    position: absolute;
    top: 1.2%;
    bottom: 1.2%;
    left: 50%;
    width: 3px;
    transform: translateX(-50%);
    z-index: 60;
    pointer-events: none;
    background: linear-gradient(180deg, transparent, rgba(0, 0, 0, 0.85) 18%, rgba(0, 0, 0, 0.9) 50%, rgba(0, 0, 0, 0.85) 82%, transparent);
    filter: drop-shadow(0 0 12px rgba(0, 0, 0, 0.65));
}

.book-spine::after {
    content: "";
    position: absolute;
    top: 0;
    bottom: 0;
    left: 1px;
    width: 1px;
    background: linear-gradient(180deg, transparent, rgba(148, 163, 184, 0.22), transparent);
}

.book-stack {
    position: absolute;
    top: 1.4%;
    bottom: 1.4%;
    pointer-events: none;
}

.book-stack i {
    position: absolute;
    top: 0;
    bottom: 0;
    border: 1px solid rgba(148, 163, 184, 0.14);
    background: linear-gradient(180deg, #121724, #0C0F17);
}

.book-stack-right {
    right: 0;
    width: 12px;
}

.book-stack-right i {
    right: 0;
    width: 100%;
    border-radius: 0 10px 10px 0;
}

.book-stack-right i:nth-child(1) { transform: translate(9px, 4px); }
.book-stack-right i:nth-child(2) { transform: translate(6px, 2px); }
.book-stack-right i:nth-child(3) { transform: translate(3px, 1px); }

.book-stack-left {
    left: 0;
    width: 12px;
}

.book-stack-left i {
    left: 0;
    width: 100%;
    border-radius: 10px 0 0 10px;
}

.book-stack-left i:nth-child(1) { transform: translate(-9px, 4px); }
.book-stack-left i:nth-child(2) { transform: translate(-6px, 2px); }
.book-stack-left i:nth-child(3) { transform: translate(-3px, 1px); }

.page-under-shadow {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 50%;
    right: 0;
    z-index: 55;
    pointer-events: none;
    opacity: 0;
    background: linear-gradient(90deg, rgba(0, 0, 0, 0.9), rgba(0, 0, 0, 0.28) 34%, rgba(0, 0, 0, 0.05) 70%, transparent);
}

.book-shadow {
    position: absolute;
    left: 8%;
    right: 8%;
    bottom: -26px;
    height: 42px;
    z-index: -1;
    pointer-events: none;
    background: radial-gradient(50% 100% at 50% 50%, rgba(0, 0, 0, 0.75), transparent 72%);
    filter: blur(10px);
}

.scroll-hint {
    position: absolute;
    left: 50%;
    bottom: 58px;
    transform: translateX(-50%);
    z-index: 6;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 4px;
    color: var(--text-muted);
    font-size: 9.5px;
    letter-spacing: 0.3em;
    text-transform: uppercase;
    opacity: 0;
    pointer-events: none;
}

.scroll-hint.is-visible {
    opacity: 1;
}

.scroll-hint i {
    animation: hint-bounce 1.8s ease-in-out infinite;
}