/* ===========================
   CSS Variables
   =========================== */
:root {
    --primary-color: #2c3e50;
    --secondary-color: #1abc9c;
    --accent-color: #16a085;
    --text-dark: #333333;
    --text-light: #666666;
    --text-white: #ffffff;
    --bg-light: #f8f9fa;
    --bg-dark: #1a1a1a;
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
    --transition: all 0.3s ease;
}

/* ===========================
   Global Styles
   =========================== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Noto Sans KR', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    line-height: 1.7;
    color: var(--text-dark);
    background-color: #ffffff;
    overflow-x: hidden;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* ===========================
   Navigation
   =========================== */
.navbar {
    position: fixed;
    top: 0;
    width: 100%;
    background: rgba(255, 255, 255, 0.98);
    backdrop-filter: blur(10px);
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    z-index: 1000;
    transition: var(--transition);
}

.navbar .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 20px;
}

.nav-brand {
    font-size: 1.3rem;
    font-weight: 700;
    color: var(--primary-color);
    font-family: 'Playfair Display', serif;
}

.nav-right {
    display: flex;
    align-items: center;
    gap: 2rem;
}

.website-link {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    color: var(--text-dark);
    font-weight: 500;
    font-size: 0.9rem;
    padding: 6px 12px;
    border-radius: 20px;
    transition: var(--transition);
}

.website-link:hover {
    color: var(--secondary-color);
    background: var(--bg-light);
}

.website-link i {
    color: var(--secondary-color);
}

.lang-switcher {
    display: flex;
    gap: 0.5rem;
    background: var(--bg-light);
    padding: 5px;
    border-radius: 25px;
}

.lang-btn {
    padding: 6px 14px;
    border: none;
    background: transparent;
    color: var(--text-dark);
    font-weight: 600;
    font-size: 0.85rem;
    border-radius: 20px;
    cursor: pointer;
    transition: var(--transition);
    font-family: 'Noto Sans KR', sans-serif;
}

.lang-btn.active {
    background: var(--secondary-color);
    color: var(--text-white);
}

.lang-btn:hover {
    background: var(--accent-color);
    color: var(--text-white);
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 1.5rem;
}

.nav-menu a {
    text-decoration: none;
    color: var(--text-dark);
    font-weight: 500;
    font-size: 0.95rem;
    transition: var(--transition);
    position: relative;
}

.nav-menu a::after {
    content: '';
    position: absolute;
    bottom: -5px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--secondary-color);
    transition: var(--transition);
}

.nav-menu a:hover {
    color: var(--secondary-color);
}

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

.nav-toggle {
    display: none;
    font-size: 1.5rem;
    color: var(--primary-color);
    cursor: pointer;
}

/* ===========================
   Hero Section
   =========================== */
.hero {
    position: relative;
    background: #ffffff;
    min-height: 50vh;
    display: flex;
    align-items: center;
    padding: 120px 20px 60px;
    overflow: hidden;
}

.hero-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    gap: 1rem;
    width: 100%;
}

.hero-text {
    color: var(--text-dark);
}

.hero-title {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
    font-family: 'Playfair Display', serif;
    line-height: 1.2;
}

.hero-subtitle {
    font-size: 1.3rem;
    font-weight: 500;
    color: var(--secondary-color);
}

/* ===========================
   Section Styles
   =========================== */
.section {
    padding: 60px 20px;
}

.section-header {
    text-align: center;
    margin-bottom: 40px;
}

.section-title {
    font-size: 2rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-family: 'Playfair Display', serif;
}

.section-divider {
    width: 60px;
    height: 3px;
    background: var(--secondary-color);
    margin: 0 auto;
    border-radius: 2px;
}

/* ===========================
   Content List (Unified Style)
   =========================== */
.content-list {
    display: flex;
    flex-direction: column;
    gap: 15px;
    max-width: 900px;
    margin: 0 auto;
}

.content-item {
    background: #ffffff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.08);
    transition: var(--transition);
    border-left: 3px solid var(--secondary-color);
    display: flex;
    align-items: flex-start;
    gap: 15px;
}

.content-item:hover {
    transform: translateX(5px);
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.12);
}

.content-item p {
    color: var(--text-dark);
    line-height: 1.7;
    font-size: 0.95rem;
    margin: 0;
    flex: 1;
}

.year-badge {
    flex-shrink: 0;
    background: var(--secondary-color);
    color: var(--text-white);
    padding: 5px 12px;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: 600;
    white-space: nowrap;
}

/* ===========================
   Education Section
   =========================== */
.education-section {
    background: var(--bg-light);
}

/* ===========================
   Experience Section
   =========================== */
.experience-section {
    background: #ffffff;
}

/* ===========================
   Research Section
   =========================== */
.research-section {
    background: var(--bg-light);
}

.research-category {
    margin-bottom: 40px;
}

.category-title {
    color: var(--secondary-color);
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 20px;
    padding-bottom: 8px;
    border-bottom: 2px solid var(--secondary-color);
    display: inline-block;
}

/* ===========================
   Reports Section
   =========================== */
.reports-section {
    background: #ffffff;
}

/* ===========================
   Activities Section
   =========================== */
.activities-section {
    background: var(--bg-light);
}

/* ===========================
   Publications Section
   =========================== */
.publications-section {
    background: #ffffff;
}

.publications-container {
    display: flex;
    flex-direction: column;
    gap: 40px;
}

.publication-category {
    background: var(--bg-light);
    padding: 25px;
    border-radius: 12px;
}

.publication-category h3 {
    color: var(--primary-color);
    font-size: 1.4rem;
    margin-bottom: 20px;
    font-weight: 600;
}

.lecture-list {
    list-style: none;
    padding-left: 0;
    margin-top: 10px;
}

.lecture-list li {
    padding: 8px 0;
    padding-left: 20px;
    color: var(--text-dark);
    position: relative;
    line-height: 1.6;
    font-size: 0.95rem;
}

.lecture-list li::before {
    content: '▸';
    position: absolute;
    left: 0;
    color: var(--secondary-color);
    font-weight: 700;
}

/* ===========================
   Footer
   =========================== */
.footer {
    background: var(--primary-color);
    color: var(--text-white);
    padding: 30px 20px;
    text-align: center;
}

.footer-content p {
    color: rgba(255, 255, 255, 0.8);
    font-size: 0.9rem;
}

/* ===========================
   Responsive Design - Mobile First
   =========================== */
@media (max-width: 768px) {
    /* Navigation */
    .navbar .container {
        padding: 0.8rem 15px;
    }

    .nav-brand {
        font-size: 1.1rem;
    }

    .nav-right {
        gap: 0.8rem;
    }

    .website-link {
        display: none;
    }

    .lang-switcher {
        order: 2;
    }

    .nav-menu {
        position: fixed;
        top: 65px;
        left: -100%;
        width: 100%;
        flex-direction: column;
        background: rgba(255, 255, 255, 0.98);
        padding: 20px;
        gap: 0;
        box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
        transition: var(--transition);
        max-height: calc(100vh - 65px);
        overflow-y: auto;
    }

    .nav-menu.active {
        left: 0;
    }

    .nav-menu li {
        padding: 12px 0;
        border-bottom: 1px solid rgba(0, 0, 0, 0.05);
    }

    .nav-menu a {
        font-size: 1rem;
    }

    .nav-toggle {
        display: block;
        order: 1;
    }

    /* Hero Section */
    .hero {
        min-height: 40vh;
        padding: 100px 15px 40px;
    }

    .hero-title {
        font-size: 1.8rem;
    }

    .hero-subtitle {
        font-size: 1.1rem;
    }

    /* Sections */
    .section {
        padding: 40px 15px;
    }

    .section-title {
        font-size: 1.6rem;
    }

    /* Content Items */
    .content-item {
        flex-direction: column;
        padding: 15px;
        gap: 10px;
    }

    .year-badge {
        align-self: flex-start;
    }

    .content-item p {
        font-size: 0.9rem;
    }

    /* Research Category */
    .category-title {
        font-size: 1.3rem;
    }

    /* Publications */
    .publication-category {
        padding: 20px 15px;
    }

    .publication-category h3 {
        font-size: 1.2rem;
    }

    /* Footer */
    .footer {
        padding: 25px 15px;
    }
}

@media (max-width: 480px) {
    .nav-brand {
        font-size: 1rem;
    }

    .lang-btn {
        padding: 5px 10px;
        font-size: 0.8rem;
    }

    .hero-title {
        font-size: 1.5rem;
    }

    .hero-subtitle {
        font-size: 1rem;
    }

    .section-title {
        font-size: 1.4rem;
    }

    .content-item {
        padding: 12px;
    }

    .content-item p {
        font-size: 0.85rem;
    }

    .year-badge {
        font-size: 0.8rem;
        padding: 4px 10px;
    }
}

/* ===========================
   Tablet Optimization
   =========================== */
@media (min-width: 769px) and (max-width: 1024px) {
    .container {
        padding: 0 30px;
    }

    .nav-menu {
        gap: 1.2rem;
    }

    .nav-menu a {
        font-size: 0.9rem;
    }

    .website-link {
        font-size: 0.85rem;
    }

    .hero-title {
        font-size: 2.2rem;
    }
}