.section-bg {
            background:
                radial-gradient(ellipse 60% 40% at 15% 20%, rgba(20, 35, 102, 0.5) 0%, transparent 60%),
                radial-gradient(ellipse 55% 45% at 85% 80%, rgba(30, 58, 138, 0.4) 0%, transparent 60%),
                linear-gradient(165deg, #050B26 0%, #0A1647 55%, #0B1B5C 100%);
        }

        .title-display {
            font-family: var(--font-display);
            letter-spacing: -0.005em;
            line-height: 1;
        }
        .title-underline {
            display: inline-block;
            height: 3px;
            background: linear-gradient(90deg,
                rgba(255, 255, 255, 0.95) 0%,
                rgba(127, 200, 248, 0.85) 40%,
                rgba(127, 200, 248, 0) 100%);
            border-radius: 2px;
            box-shadow: 0 0 18px rgba(127, 200, 248, 0.55);
        }

        /* ---------- PDF card ---------- */
        .pdf-card {
            display: flex;
            flex-direction: column;
            position: relative;
        }

        /* The book-cover: vertical 3:4 aspect, slight 3D feel */
        .pdf-cover {
            position: relative;
            width: 100%;
            aspect-ratio: 3 / 4;
            border-radius: 12px;
            overflow: hidden;
            background: linear-gradient(180deg, #0E1E5C 0%, #060F33 100%);
            border: 1px solid rgba(127, 200, 248, 0.22);
            box-shadow:
                0 24px 50px rgba(0, 0, 0, 0.5),
                0 0 0 1px rgba(255, 255, 255, 0.03) inset,
                0 0 35px rgba(127, 200, 248, 0.1) inset;
            transition: transform 0.4s cubic-bezier(.2,.7,.2,1),
                        box-shadow 0.4s cubic-bezier(.2,.7,.2,1),
                        border-color 0.3s ease;
            cursor: pointer;
        }
        /* The "spine" effect — a faint vertical line on the left */
        .pdf-cover::before {
            content: "";
            position: absolute;
            top: 0;
            bottom: 0;
            left: 0;
            width: 14px;
            background: linear-gradient(90deg,
                rgba(0, 0, 0, 0.45) 0%,
                rgba(255, 255, 255, 0.05) 60%,
                transparent 100%);
            pointer-events: none;
            z-index: 2;
        }
        /* Subtle top highlight */
        .pdf-cover::after {
            content: "";
            position: absolute;
            inset: 0;
            background: linear-gradient(180deg,
                rgba(255, 255, 255, 0.08) 0%,
                transparent 25%,
                transparent 80%,
                rgba(0, 0, 0, 0.35) 100%);
            pointer-events: none;
            z-index: 1;
        }
        .pdf-card:hover .pdf-cover {
            transform: translateY(-4px) rotate(-0.5deg);
            border-color: rgba(127, 200, 248, 0.5);
            box-shadow:
                0 32px 60px rgba(0, 0, 0, 0.6),
                0 0 0 1px rgba(127, 200, 248, 0.25) inset,
                0 0 50px rgba(127, 200, 248, 0.28);
        }
        .pdf-cover img {
            display: block;
            width: 100%;
            height: 100%;
            object-fit: cover;
        }

        /* Placeholder cover with decorative architecture */
        .pdf-cover-ph {
            width: 100%;
            height: 100%;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: space-between;
            padding: 1.4rem 1.2rem;
            position: relative;
            color: rgba(184, 220, 251, 0.9);
        }
        .pdf-cover-ph .ph-top {
            text-align: center;
            font-family: var(--font-body);
            font-size: 0.62rem;
            font-weight: 800;
            letter-spacing: 0.18em;
            text-transform: uppercase;
            color: rgba(184, 220, 251, 0.85);
            line-height: 1.5;
            max-width: 90%;
            position: relative;
            z-index: 2;
        }
        .pdf-cover-ph .ph-title {
            font-family: var(--font-display);
            font-size: 1.25rem;
            letter-spacing: 0.02em;
            color: #fff;
            text-align: center;
            line-height: 1.1;
            position: relative;
            z-index: 2;
            text-shadow: 0 2px 18px rgba(127, 200, 248, 0.4);
            background-image:
                repeating-linear-gradient(45deg, rgba(255,255,255,0.95) 0 1.5px, transparent 1.5px 5px),
                repeating-linear-gradient(-45deg, rgba(255,255,255,0.95) 0 1.5px, transparent 1.5px 5px),
                radial-gradient(circle at center, #ffffff 0%, #d6e4ff 100%);
            -webkit-background-clip: text;
            background-clip: text;
            color: transparent;
            -webkit-text-stroke: 1px rgba(255,255,255,0.15);
            filter: drop-shadow(0 2px 10px rgba(127, 200, 248, 0.3));
        }
        .pdf-cover-ph .ph-foot {
            font-family: var(--font-body);
            font-size: 0.58rem;
            font-weight: 700;
            letter-spacing: 0.16em;
            color: var(--c-accent);
            text-transform: uppercase;
            position: relative;
            z-index: 2;
            text-align: center;
            line-height: 1.4;
        }
        .pdf-cover-ph .ph-architecture {
            position: absolute;
            left: 0; right: 0; bottom: 0;
            opacity: 0.4;
            mix-blend-mode: screen;
            pointer-events: none;
        }
        /* Page corner fold */
        .corner-fold {
            position: absolute;
            top: 0;
            right: 0;
            width: 38px;
            height: 38px;
            background: linear-gradient(225deg,
                rgba(127, 200, 248, 0.65) 0%,
                rgba(127, 200, 248, 0.25) 45%,
                transparent 50%);
            border-bottom-left-radius: 8px;
            pointer-events: none;
            z-index: 3;
        }
        .corner-fold::after {
            content: "PDF";
            position: absolute;
            top: 6px;
            right: 5px;
            color: #0A1647;
            font-family: var(--font-display);
            font-size: 0.55rem;
            font-weight: 800;
            letter-spacing: 0.05em;
        }

        /* Card title */
        .pdf-title {
            margin-top: 1rem;
            color: #fff;
            font-family: var(--font-body);
            font-weight: 700;
            font-size: 0.95rem;
            line-height: 1.4;
            letter-spacing: 0.005em;
            min-height: 2.6em;
        }
        @media (min-width: 768px) {
            .pdf-title { font-size: 1rem; }
        }
        .pdf-sub {
            margin-top: 0.3rem;
            color: rgba(184, 220, 251, 0.8);
            font-size: 0.72rem;
            font-weight: 700;
            letter-spacing: 0.08em;
            text-transform: uppercase;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
        }
        .pdf-sub::before {
            content: "";
            width: 5px;
            height: 5px;
            border-radius: 9999px;
            background: var(--c-accent);
            box-shadow: 0 0 8px var(--c-accent);
        }

        /* Action buttons (read + download) */
        .pdf-actions {
            display: flex;
            gap: 0.6rem;
            margin-top: 0.85rem;
        }
        .pdf-btn {
            flex: 1;
            display: inline-flex;
            align-items: center;
            justify-content: center;
            gap: 0.45rem;
            padding: 0.6rem 0.85rem;
            border-radius: 10px;
            font-family: var(--font-body);
            font-weight: 700;
            font-size: 0.78rem;
            letter-spacing: 0.04em;
            transition: all 0.25s cubic-bezier(.2,.7,.2,1);
            cursor: pointer;
            border: 1px solid transparent;
            white-space: nowrap;
        }
        .pdf-btn-read {
            background: rgba(127, 200, 248, 0.12);
            color: var(--c-accent-soft);
            border-color: rgba(127, 200, 248, 0.35);
        }
        .pdf-btn-read:hover {
            background: rgba(127, 200, 248, 0.22);
            color: #fff;
            border-color: var(--c-accent);
            box-shadow: 0 6px 18px rgba(127, 200, 248, 0.25);
        }
        .pdf-btn-download {
            background: var(--c-accent-soft);
            color: #0A1647;
            border-color: rgba(127, 200, 248, 0.6);
        }
        .pdf-btn-download:hover {
            background: #CFE7FC;
            transform: translateY(-1px);
            box-shadow: 0 8px 20px rgba(127, 200, 248, 0.35);
        }
        /* Icon-only mode (when label is empty) */
        .pdf-btn.is-icon-only {
            flex: 0 0 auto;
            width: 42px;
            padding: 0.6rem;
        }

        /* PDF reader modal */
        .pdf-modal {
            position: fixed;
            inset: 0;
            z-index: 100;
            background: rgba(5, 11, 38, 0.95);
            backdrop-filter: blur(8px);
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 1.25rem;
            opacity: 0;
            pointer-events: none;
            transition: opacity 0.3s ease;
        }
        .pdf-modal.is-open {
            opacity: 1;
            pointer-events: auto;
        }
        .pdf-modal-content {
            position: relative;
            width: 100%;
            max-width: 1100px;
            height: 90vh;
            background: #0A1647;
            border-radius: 16px;
            border: 1px solid rgba(127, 200, 248, 0.3);
            box-shadow: 0 40px 80px rgba(0, 0, 0, 0.6);
            display: flex;
            flex-direction: column;
            overflow: hidden;
        }
        .pdf-modal-head {
            display: flex;
            align-items: center;
            justify-content: space-between;
            gap: 1rem;
            padding: 0.85rem 1rem;
            border-bottom: 1px solid rgba(127, 200, 248, 0.18);
            background: rgba(11, 22, 64, 0.7);
        }
        .pdf-modal-title {
            font-weight: 700;
            color: #fff;
            font-size: 0.95rem;
            line-height: 1.3;
            flex: 1;
            min-width: 0;
            overflow: hidden;
            text-overflow: ellipsis;
            white-space: nowrap;
        }
        .pdf-modal-actions { display: flex; gap: 0.5rem; flex-shrink: 0; }
        .pdf-modal-body { flex: 1; overflow: hidden; background: #0a1340; }
        .pdf-modal-body iframe { width: 100%; height: 100%; border: 0; }
        .pdf-modal-body .pdf-fallback {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            height: 100%;
            color: rgba(255, 255, 255, 0.7);
            text-align: center;
            padding: 2rem;
            gap: 1rem;
        }

        body.no-scroll { overflow: hidden; }

        /* ---------- Animations ---------- */
        @keyframes riseIn {
            from { opacity: 0; transform: translateY(16px); }
            to   { opacity: 1; transform: translateY(0); }
        }
        @keyframes drawLine { from { transform: scaleX(0); } to { transform: scaleX(1); } }
        .anim-rise { opacity: 0; animation: riseIn 0.85s cubic-bezier(.2,.7,.2,1) forwards; }
        .anim-line { transform-origin: left center; transform: scaleX(0); animation: drawLine 0.9s cubic-bezier(.2,.7,.2,1) 0.35s forwards; }

        /* ---------- Sizing ---------- */
        .title-size { font-size: clamp(1.9rem, 5vw, 4rem); }