/* ===========================
   Root & Global
   =========================== */
:root {
    --primary: #0050a8;
    --primary-dark: #00356f;
    --primary-light: #e7f1ff;
    --accent: #ffb400;

    --bg-main: #f3f5fb;
    --bg-card: #ffffff;
    --bg-alt: #f9fafc;

    --border-color: #dde3f0;

    --text-main: #1f2933;
    --text-muted: #6b7280;
    --text-invert: #ffffff;

    --radius-sm: 6px;
    --radius: 12px;
    --radius-lg: 20px;

    --shadow-sm: 0 2px 6px rgba(15, 23, 42, 0.08);
    --shadow-md: 0 8px 20px rgba(15, 23, 42, 0.12);
    --shadow-lg: 0 18px 45px rgba(15, 23, 42, 0.22);

    --transition-fast: 0.18s ease-out;
    --transition: 0.25s ease;

    --container-width: 1180px;
}

/* Reset */
*,
*::before,
*::after {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    margin: 0;
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    background: radial-gradient(circle at top left, #ffffff 0, #f3f5fb 45%, #e5ecfb 100%);
    color: var(--text-main);
    line-height: 1.6;
}

/* Base elements */
img {
    max-width: 100%;
    display: block;
}

a {
    color: inherit;
    text-decoration: none;
}
/* Link trong phần nội dung (vd: ссылки на внешние проекты) */
.text-link {
    font-weight: 600;                 /* đậm hơn */
    color: var(--primary);            /* dùng màu chủ đạo của site */
    text-decoration: underline;       /* gạch chân */
    text-decoration-thickness: 1.5px; /* gạch chân dày hơn chút cho rõ */
    text-underline-offset: 3px;       /* gạch cách chữ một chút */
    cursor: pointer;
}

.text-link:hover {
    color: var(--primary-dark);       /* hover đậm hơn một chút */
}


ul {
    margin: 0;
    padding: 0;
    list-style: none;
}

p {
    margin: 0 0 0.6rem;
}

/* Container & Sections */
.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 1.5rem;
}

.section {
    padding: 4rem 0;
}

.section:nth-of-type(even) {
    background: var(--bg-alt);
}

.section-title {
    font-size: 1.8rem;
    font-weight: 600;
    margin-bottom: 2rem;
    color: var(--primary-dark);
    position: relative;
    display: inline-block;
    padding-bottom: 0.4rem;
}

.section-title::after {
    content: "";
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    bottom: 0;
    width: 56px;
    height: 3px;
    border-radius: 999px;
    background: linear-gradient(90deg, var(--accent), var(--primary));
}

/* ===========================
   Navigation
   =========================== */
.navbar {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(14px);
    border-bottom: 1px solid rgba(221, 227, 240, 0.8);
    box-shadow: var(--shadow-sm);
}

.nav-wrapper {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 2rem;
    padding: 0.8rem 0;
}

.logo {
    font-size: 1.1rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    color: var(--primary-dark);
    white-space: nowrap;
}

.nav-links {
    display: flex;
    gap: 1.4rem;
    font-size: 0.95rem;
    color: var(--text-muted);
    flex-wrap: wrap;
    justify-content: flex-end;
}

.nav-links a {
    position: relative;
    padding-bottom: 0.25rem;
    transition: color var(--transition-fast);
}

.nav-links a::after {
    content: "";
    position: absolute;
    left: 0;
    bottom: 0;
    height: 2px;
    width: 0;
    border-radius: 999px;
    background: linear-gradient(90deg, var(--accent), var(--primary));
    transition: width var(--transition-fast);
}

.nav-links a:hover {
    color: var(--primary-dark);
}

.nav-links a:hover::after {
    width: 100%;
}

/* ===========================
   Intro / Hero
   =========================== */
.intro-section {
    padding-top: 4.5rem;
    padding-bottom: 4.5rem;
}

.intro-layout {
    display: grid;
    grid-template-columns: minmax(0, 1.25fr) minmax(0, 1fr);
    gap: 3rem;
    align-items: center;
}

.badge {
    display: inline-flex;
    align-items: center;
    padding: 0.15rem 0.75rem;
    border-radius: 999px;
    background: rgba(37, 99, 235, 0.08);
    border: 1px solid rgba(37, 99, 235, 0.25);
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    color: var(--primary-dark);
    margin-bottom: 0.8rem;
}

.title-large {
    font-size: 2.05rem;        /* nhỏ đi chút để câu dài hơn, ít xuống dòng */
    align-items: center;
    justify-content: center;
    font-weight: 650;
    color: var(--primary-dark);
    line-height: 1.5;         /* giảm khoảng cách giữa các dòng */
    letter-spacing: 0.01em;    /* chữ gọn hơn một chút */
    margin-bottom: 0.6rem;     /* bớt khoảng trắng phía dưới tiêu đề */
}


.subtitle {
    font-size: 1.05rem;
    color: var(--text-muted);
    margin-bottom: 1.4rem;
}

.intro-text {
    font-size: 1rem;
    color: var(--text-main);
    margin-bottom: 0.8rem;
    max-width: 40rem;
}

.intro-actions {
    margin-top: 1.6rem;
    display: flex;
    flex-wrap: wrap;
    gap: 0.8rem;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    font-size: 0.96rem;
    font-weight: 600;
    padding: 0.85rem 1.9rem;
    border-radius: 999px;
    border: none;
    cursor: pointer;
    transition: var(--transition);
    text-decoration: none;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary), var(--primary-dark));
    color: #ffffff;
    box-shadow: var(--shadow-md);
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-lg);
}

.btn-ghost {
    background: transparent;
    color: var(--primary-dark);
    border: 1px solid rgba(37, 99, 235, 0.3);
}

.btn-ghost:hover {
    background: rgba(37, 99, 235, 0.06);
}

/* Hero image */
.intro-image {
    position: relative;
}

.placeholder-image {
    border-radius: 24px;
    overflow: hidden;
    box-shadow: var(--shadow-lg);
    background: radial-gradient(circle at top, #dbeafe 0, #eff6ff 45%, #e0ecff 100%);
    border: 1px solid rgba(221, 227, 240, 0.8);
    position: relative;
}

.placeholder-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}

.hero-glow::before {
    content: "";
    position: absolute;
    inset: 10%;
    border-radius: inherit;
    background: radial-gradient(circle at 10% 0%, rgba(59, 130, 246, 0.28), transparent 60%);
    pointer-events: none;
}

.hero-stats {
    position: absolute;
    bottom: 1rem;
    left: 1rem;
    right: 1rem;
    display: flex;
    gap: 0.75rem;
    flex-wrap: wrap;
}

.hero-stat {
    flex: 1;
    min-width: 90px;
    background: rgba(15, 23, 42, 0.75);
    border-radius: 999px;
    padding: 0.4rem 0.7rem;
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.hero-stat-number {
    font-size: 0.9rem;
    font-weight: 600;
    color: #e5f0ff;
}

.hero-stat-label {
    font-size: 0.75rem;
    color: #bfdbfe;
}

/* ===========================
   Author Section
   =========================== */
.author-section {
    background: #f8f9ff;
}

.author-toggle {
    width: 100%;
    background: transparent;
    border: none;
    padding: 0;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 1.5rem;
}

.author-toggle .section-title {
    margin-bottom: 0;
}

.toggle-icon {
    font-size: 1.3rem;
    color: var(--text-muted);
    transition: transform var(--transition-fast);
    margin-left: 1rem;
}

.author-toggle.open .toggle-icon {
    transform: rotate(180deg);
}

.author-content {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: 1.8rem;
}

.author-card {
    display: grid;
    grid-template-columns: auto minmax(0, 1fr);
    gap: 1.6rem;
    padding: 1.5rem 1.8rem;
    border-radius: var(--radius-lg);
    background: var(--bg-card);
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(221, 227, 240, 0.9);
}

.avatar-placeholder {
    width: 110px;
    height: 110px;
    border-radius: 999px;
    background: radial-gradient(circle at 30% 0, #bfdbfe 0, #1d4ed8 40%, #0f172a 100%);
    padding: 3px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.author-image {
    width: 100%;
    height: 100%;
    border-radius: inherit;
    object-fit: cover;
}

.author-name {
    font-size: 1.2rem;
    font-weight: 600;
    margin-bottom: 0.2rem;
}

.author-role {
    font-size: 0.95rem;
    color: var(--primary-dark);
    margin-bottom: 0.2rem;
}

.author-title {
    font-size: 0.9rem;
    color: var(--text-muted);
    margin-bottom: 0.8rem;
}

.author-bio {
    font-size: 0.95rem;
    margin-bottom: 0.8rem;
    color: var(--text-main);
}

.author-stats {
    display: flex;
    gap: 1.5rem;
}

.stat-number {
    font-weight: 700;
    font-size: 1.1rem;
    color: var(--primary-dark);
}

.stat-label {
    font-size: 0.8rem;
    color: var(--text-muted);
}

/* ===========================
   Abstract
   =========================== */
.abstract-section {
    background: #ffffff;
}

.abstract-content {
    max-width: 900px;
    margin: 0 auto;
}

.abstract-text {
    font-size: 1.02rem;
    color: var(--text-main);
    line-height: 1.9;
    margin-bottom: 2.3rem;
    text-align: center;
}

.abstract-highlights {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 1.3rem;
}

.highlight-item {
    padding: 1rem 1.2rem;
    border-radius: var(--radius);
    background: var(--primary-light);
    border: 1px solid rgba(191, 219, 254, 0.7);
    box-shadow: var(--shadow-sm);
}

.highlight-item h4 {
    margin: 0 0 0.4rem;
    font-size: 0.98rem;
    color: var(--primary-dark);
}

.highlight-item p {
    font-size: 0.9rem;
    margin: 0;
    color: var(--text-main);
}

/* ===========================
   Gallery
   =========================== */
.gallery-section {
    background: #f3f5fb;
}

.gallery-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 1.6rem;
}

.gallery-item {
    background: var(--bg-card);
    border-radius: var(--radius);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(221, 227, 240, 0.9);
    cursor: pointer;
    display: flex;
    flex-direction: column;
    transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.gallery-image {
    width: 100%;
    height: 190px;
    overflow: hidden;
}

.gallery-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.gallery-caption {
    padding: 0.9rem 1rem 1rem;
    font-size: 0.9rem;
    color: var(--primary-dark);
    font-weight: 500;
    text-align: center;
}

.gallery-item:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

/* ===========================
   Video Section
   =========================== */
.video-section {
    background: #ffffff;
}

.video-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 1.6rem;
}
.video-section .video-grid {
    justify-content: center;
}

.video-card {
    background: var(--bg-card);
    border-radius: var(--radius);
    max-width: 480px;      /* giới hạn độ rộng mỗi video-card */
    margin: 0 auto;        /* căn giữa mỗi card */
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(221, 227, 240, 0.9);
    padding: 1rem;
    display: flex;
    flex-direction: column;
    gap: 0.8rem;
    transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.video-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.video-wrapper {
    position: relative;
    border-radius: 12px;
    overflow: hidden;
    background: #000;
}

.video-wrapper::before {
    content: "";
    display: block;
    padding-top: 100%; /* thử 56.25% hoặc 50% nếu muốn thấp hơn */
}

.video-element {
    position: absolute;
    inset: 0;
    width: 100%;
    height: 140%;
    object-fit: cover;
}

.play-button-overlay {
    position: absolute;
    inset: 0;
    margin: auto;
    width: 56px;
    height: 56px;
    border-radius: 999px;
    border: none;
    cursor: pointer;
    background: radial-gradient(circle at 30% 0, #ffffff 0, #fbbf24 40%, #b45309 100%);
    color: #111827;
    font-size: 1.4rem;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 12px 30px rgba(0, 0, 0, 0.35);
    transition: transform var(--transition-fast), box-shadow var(--transition-fast), opacity var(--transition-fast);
    opacity: 0.9;
}

.play-button-overlay:hover {
    transform: scale(1.05);
    box-shadow: 0 18px 45px rgba(0, 0, 0, 0.5);
    opacity: 1;
}

.video-title {
    font-size: 0.94rem;
    color: var(--text-main);
    text-align: center;
}

/* ===========================
   Slides / Presentation Section
   =========================== */
.slides-section {
    background: #ffffff;
}

.slides-layout {
    display: grid;
    grid-template-columns: minmax(0, 0.95fr) minmax(0, 1.2fr);
    gap: 2rem;
    align-items: flex-start;
}

.slides-subtitle {
    margin: 0 0 0.6rem;
    font-size: 1.1rem;
    color: var(--primary-dark);
}

.slides-text {
    font-size: 0.95rem;
    color: var(--text-main);
    margin-bottom: 0.6rem;
}

.slides-actions {
    margin-top: 1.2rem;
    display: flex;
    flex-wrap: wrap;
    gap: 0.8rem;
}

/* Khung PDF */
.slides-viewer {
    width: 100%;
}

.slides-frame-wrapper {
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-md);
    border: 1px solid rgba(221, 227, 240, 0.9);
    background: #0b1120;
    position: relative;
}

/* Giữ tỷ lệ khung 16:9 gần giống slide */
.slides-frame-wrapper::before {
    content: "";
    display: block;
    padding-top: 56.25%; /* 16:9 */
}

.slides-frame {
    position: absolute;
    inset: 0;
    width: 100%;
    height: 100%;
    border: none;
    background: #111827;
}

.slides-note {
    margin-top: 0.6rem;
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* Responsive */
@media (max-width: 1024px) {
    .slides-layout {
        grid-template-columns: minmax(0, 1fr);
    }
}

@media (max-width: 768px) {
    .slides-actions {
        flex-direction: column;
        align-items: stretch;
    }
}


/* ===========================
   Details
   =========================== */
.details-section {
    background: #f8f9ff;
}

.details-grid {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 1.6rem;
}

.detail-card {
    background: var(--bg-card);
    border-radius: var(--radius);
    padding: 1.2rem 1.3rem;
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(221, 227, 240, 0.9);
    text-align: left;
}

.detail-icon {
    width: 40px;
    height: 40px;
    border-radius: 999px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--primary-light);
    margin-bottom: 0.7rem;
    font-size: 1.1rem;
}

.detail-card h3 {
    margin: 0 0 0.4rem;
    font-size: 1rem;
    color: var(--primary-dark);
}

.detail-card p {
    font-size: 0.9rem;
    color: var(--text-main);
}

/* ===========================
   Footer
   =========================== */
.footer {
    background: #0b1220;
    color: #e5e7eb;
    padding-top: 2.8rem;
}

.footer-content {
    display: grid;
    grid-template-columns: 2fr 1fr 1.4fr;
    gap: 2rem;
    padding-bottom: 2rem;
}

.footer-section h4 {
    margin: 0 0 0.8rem;
    font-size: 1rem;
}

.footer-section p,
.footer-section li {
    font-size: 0.9rem;
    color: #9ca3af;
}

.footer-section ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.footer-section a {
    color: #e5e7eb;
}

.footer-section a:hover {
    color: var(--accent);
}

.footer-bottom {
    border-top: 1px solid rgba(55, 65, 81, 0.8);
    padding: 0.9rem 0 1.6rem;
    text-align: center;
    font-size: 0.82rem;
    color: #9ca3af;
}

/* ===========================
   Modals
   =========================== */
.modal {
    position: fixed;
    inset: 0;
    background: rgba(15, 23, 42, 0.65);
    display: none;
    align-items: center;
    justify-content: center;
    padding: 2rem 1.5rem;
    z-index: 2000;
}

.modal.open {
    display: flex;
}

.modal-content {
    position: relative;
    max-width: 900px;
    width: 100%;
    max-height: 90vh;
    overflow-y: auto;
    background: #ffffff;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    padding: 1.8rem 2rem;
}

.modal-image {
    width: 100%;
    border-radius: var(--radius);
    margin-bottom: 1rem;
}

.modal-title {
    margin: 0 0 1rem;
    color: var(--primary-dark);
    font-size: 1.4rem;
}

.modal-description {
    font-size: 0.95rem;
    color: var(--text-main);
    line-height: 1.7;
}

.modal-description ul {
    margin: 0.5rem 0 0;
    padding-left: 1.3rem;
    list-style: disc;
}

.modal-description li {
    margin-bottom: 0.25rem;
}

.modal-close {
    position: absolute;
    right: 1.2rem;
    top: 1rem;
    cursor: pointer;
    font-size: 1.6rem;
    color: var(--text-muted);
    transition: color 0.2s ease;
}

.modal-close:hover {
    color: var(--primary-dark);
}

/* ===========================
   Scroll-to-top button
   =========================== */
#scrollToTop {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    background-color: var(--primary);
    color: white;
    border: none;
    border-radius: 50%;
    font-size: 1.5rem;
    cursor: pointer;
    display: none;
    z-index: 999;
    box-shadow: 0 4px 12px rgba(0, 80, 168, 0.3);
    transition: all 0.3s ease;
    align-items: center;
    justify-content: center;
}

/* ===========================
   Animations & Scroll
   =========================== */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.animate-on-scroll {
    opacity: 0;
    transform: translateY(20px);
}

/* ===========================
   Responsive
   =========================== */
@media (max-width: 1024px) {
    .intro-layout {
        grid-template-columns: minmax(0, 1.1fr) minmax(0, 0.9fr);
        gap: 2rem;
    }

    .gallery-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

    .details-grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }

    .footer-content {
        grid-template-columns: 1.5fr 1fr;
    }

    .abstract-highlights {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}

@media (max-width: 768px) {
    .nav-wrapper {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.6rem;
    }

    .intro-layout {
        grid-template-columns: minmax(0, 1fr);
    }

    .intro-image {
        order: -1;
    }


    .abstract-content {
        grid-template-columns: minmax(0, 1fr);
    }

    .gallery-grid,
    .video-grid,
    .details-grid {
        grid-template-columns: minmax(0, 1fr);
    }

    .author-card {
        grid-template-columns: minmax(0, 1fr);
    }

    .avatar-placeholder {
        width: 120px;
        height: 120px;
        margin-bottom: 0.5rem;
    }

    .footer-content {
        grid-template-columns: minmax(0, 1fr);
    }
}

@media (max-width: 480px) {
    .section {
        padding: 3rem 0;
    }

    .logo {
        font-size: 1rem;
    }

    .nav-links {
        gap: 0.8rem;
        font-size: 0.86rem;
        flex-wrap: wrap;
    }

    .gallery-image {
        height: 170px;
    }

    .modal-content {
        padding: 1.4rem 1.3rem;
    }
}
.intro-text {
    text-align: justify;
    margin-bottom: 0.2em;
}

.intro-indent {
    text-indent: 1em;      /* thụt đầu dòng đoạn văn */
}

.intro-list {
    margin-left: 2.5em;    /* thụt vào so với lề trái */
    margin-bottom: 1em;
    padding-left: 1em;
}
.intro-list li {
    margin-bottom: 0.3em;
}