/* ===========================
   CSS Variables & Reset
   =========================== */

:root {
    /* Carbon Charcoal Background Hierarchy */
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --nav-bg: rgba(13, 17, 23, 0.95);
    --card-bg: #161b22;

    /* Carbon Charcoal Text Colors */
    --text-primary: #c9d1d9;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;

    /* Greyscale Accent Colors */
    --accent-primary: #d1d5db;
    --accent-hover: #f3f4f6;
    --accent-success: #9ca3af;
    --accent-grey: #e5e7eb;

    /* Carbon Charcoal Borders & Shadows */
    --border-color: #30363d;
    --shadow: rgba(0, 0, 0, 0.5);
    --shadow-hover: rgba(0, 0, 0, 0.7);

    /* Typography */
    --font-primary: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-mono: 'Monaco', 'Courier New', monospace;

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 2rem;
    --spacing-lg: 4rem;
    --spacing-xl: 6rem;

    /* Transitions */
    --transition: all 0.3s ease;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: var(--font-primary);
    background-color: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.7;
    transition: var(--transition);
}

/* ===========================
   Navigation
   =========================== */

#navbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background-color: var(--nav-bg);
    backdrop-filter: blur(10px);
    z-index: 1000;
    border-bottom: 1px solid var(--border-color);
    transition: var(--transition);
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.nav-logo {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-primary);
}

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

.nav-links a {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    transition: var(--transition);
    position: relative;
}

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

.nav-links a::after {
    content: '';
    position: absolute;
    bottom: -4px;
    left: 0;
    width: 0;
    height: 2px;
    background-color: var(--accent-primary);
    transition: width 0.3s ease;
}

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

/* Hamburger Menu */
.hamburger {
    display: none;
    flex-direction: column;
    cursor: pointer;
    gap: 4px;
}

.hamburger span {
    width: 25px;
    height: 3px;
    background-color: var(--text-primary);
    transition: var(--transition);
}

/* ===========================
   Hero Section
   =========================== */

.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-lg) var(--spacing-md);
    background: linear-gradient(135deg, #0d1117 0%, #161b22 100%);
}

.hero-content {
    text-align: center;
    max-width: 800px;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 800;
    margin-bottom: var(--spacing-sm);
    background: linear-gradient(135deg, #d1d5db, #e5e7eb);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.5rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    font-weight: 500;
}

.hero-description {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
    line-height: 1.8;
}

.hero-buttons {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

/* ===========================
   Buttons
   =========================== */

.btn {
    display: inline-block;
    padding: 0.875rem 2rem;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    transition: var(--transition);
    border: 2px solid transparent;
}

.btn-primary {
    background-color: var(--accent-primary);
    color: white;
}

.btn-primary:hover {
    background-color: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: 0 10px 20px var(--shadow-hover);
}

.btn-secondary {
    background-color: transparent;
    color: var(--accent-primary);
    border-color: var(--accent-primary);
}

.btn-secondary:hover {
    background-color: var(--accent-primary);
    color: white;
    transform: translateY(-2px);
}

/* ===========================
   Sections
   =========================== */

.section {
    padding: var(--spacing-xl) var(--spacing-md);
}

.section-alt {
    background-color: var(--bg-secondary);
}

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

.section-title {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: var(--spacing-lg);
    text-align: center;
    position: relative;
    padding-bottom: 1rem;
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 80px;
    height: 4px;
    background: linear-gradient(90deg, #d1d5db, #e5e7eb);
    border-radius: 2px;
}

/* ===========================
   About Section
   =========================== */

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

.about-text p {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    line-height: 1.9;
}

/* ===========================
   Research Section
   =========================== */

.research-interests {
    margin-bottom: var(--spacing-lg);
}

.research-interests h3 {
    font-size: 1.75rem;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.interests-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.interest-card {
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 12px;
    border: 1px solid var(--border-color);
    transition: var(--transition);
}

.interest-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 30px var(--shadow-hover);
    border-color: var(--accent-primary);
}

.interest-card h4 {
    font-size: 1.25rem;
    margin-bottom: var(--spacing-sm);
    color: var(--accent-primary);
}

.interest-card p {
    color: var(--text-secondary);
}

.publications h3 {
    font-size: 1.75rem;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.publication-list {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.publication-item {
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 8px;
    border-left: 4px solid var(--accent-primary);
}

.pub-title {
    font-weight: 600;
    font-size: 1.1rem;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.pub-authors {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-bottom: 0.25rem;
}

.pub-journal {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.pub-journal a {
    color: var(--accent-primary);
    text-decoration: none;
}

.pub-journal a:hover {
    text-decoration: underline;
}

.view-all {
    margin-top: var(--spacing-md);
    text-align: center;
}

.view-all a {
    color: var(--accent-primary);
    text-decoration: none;
    font-weight: 600;
    font-size: 1.1rem;
}

.view-all a:hover {
    text-decoration: underline;
}

/* ===========================
   Projects Section
   =========================== */

.projects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: var(--spacing-md);
}

.project-card {
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 12px;
    border: 1px solid var(--border-color);
    transition: var(--transition);
    position: relative;
    display: flex;
    flex-direction: column;
}

.project-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 30px var(--shadow-hover);
    border-color: var(--accent-primary);
}

.project-card.featured {
    border: 2px solid var(--accent-primary);
    background: linear-gradient(135deg, var(--card-bg) 0%, var(--bg-secondary) 100%);
}

.project-badge {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background-color: var(--accent-primary);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: 600;
}

.project-card h3 {
    font-size: 1.5rem;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.project-role {
    color: var(--accent-primary);
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
}

.project-description {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-sm);
    flex-grow: 1;
}

.project-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    margin-bottom: var(--spacing-sm);
}

.tag {
    background-color: var(--bg-secondary);
    color: var(--text-secondary);
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.85rem;
    border: 1px solid var(--border-color);
}

.project-link {
    color: var(--accent-primary);
    text-decoration: none;
    font-weight: 600;
    display: inline-flex;
    align-items: center;
    gap: 0.25rem;
}

.project-link:hover {
    text-decoration: underline;
}

/* ===========================
   CV Section
   =========================== */

.cv-download {
    text-align: center;
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 12px;
    margin-bottom: var(--spacing-lg);
    border: 1px solid var(--border-color);
}

.cv-download p {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-sm);
    font-size: 1.1rem;
}

.cv-highlights h3 {
    font-size: 1.75rem;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.cv-section {
    margin-bottom: var(--spacing-lg);
}

.cv-section h4 {
    font-size: 1.5rem;
    margin-bottom: var(--spacing-md);
    color: var(--accent-primary);
}

.cv-item {
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 8px;
    margin-bottom: var(--spacing-sm);
    border: 1px solid var(--border-color);
}

.cv-item-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 0.5rem;
    flex-wrap: wrap;
}

.cv-item-header strong {
    font-size: 1.1rem;
    color: var(--text-primary);
}

.cv-date {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 600;
}

.cv-item p {
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-md);
}

.skill-category {
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

.skill-category strong {
    display: block;
    font-size: 1.1rem;
    margin-bottom: var(--spacing-sm);
    color: var(--accent-primary);
}

.skill-category ul {
    list-style: none;
}

.skill-category li {
    color: var(--text-secondary);
    padding: 0.25rem 0;
    padding-left: 1.5rem;
    position: relative;
}

.skill-category li::before {
    content: '▹';
    position: absolute;
    left: 0;
    color: var(--accent-primary);
    font-weight: bold;
}

/* ===========================
   Contact Section
   =========================== */

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

.contact-intro {
    text-align: center;
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-lg);
    line-height: 1.8;
}

.contact-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-md);
}

.contact-card {
    background-color: var(--card-bg);
    padding: var(--spacing-md);
    border-radius: 12px;
    border: 1px solid var(--border-color);
    text-align: center;
    transition: var(--transition);
}

.contact-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 30px var(--shadow-hover);
    border-color: var(--accent-primary);
}

.contact-card h3 {
    font-size: 1.25rem;
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.contact-card p {
    margin-bottom: 0.5rem;
}

.contact-card a {
    color: var(--accent-primary);
    text-decoration: none;
    font-weight: 500;
}

.contact-card a:hover {
    text-decoration: underline;
}

/* ===========================
   Footer
   =========================== */

footer {
    background-color: var(--bg-secondary);
    padding: var(--spacing-md);
    text-align: center;
    border-top: 1px solid var(--border-color);
}

footer p {
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
}

/* ===========================
   Responsive Design
   =========================== */

@media (max-width: 768px) {
    .nav-links {
        position: fixed;
        top: 70px;
        left: -100%;
        width: 100%;
        height: calc(100vh - 70px);
        background-color: var(--nav-bg);
        flex-direction: column;
        padding: 2rem;
        transition: left 0.3s ease;
        backdrop-filter: blur(10px);
        border-top: 1px solid var(--border-color);
    }

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

    .hamburger {
        display: flex;
    }

    .hero-title {
        font-size: 2.5rem;
    }

    .hero-subtitle {
        font-size: 1.25rem;
    }

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

    .section-title {
        font-size: 2rem;
    }

    .hero-buttons {
        flex-direction: column;
        align-items: center;
    }

    .btn {
        width: 100%;
        max-width: 300px;
        text-align: center;
    }

    .projects-grid,
    .interests-grid,
    .skills-grid,
    .contact-grid {
        grid-template-columns: 1fr;
    }

    .cv-item-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 0.5rem;
    }

    .section {
        padding: var(--spacing-lg) var(--spacing-sm);
    }

    .nav-container {
        padding: 1rem;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 2rem;
    }

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

    .section-title {
        font-size: 1.75rem;
    }
}

/* ===========================
   Utilities
   =========================== */

.text-center {
    text-align: center;
}

.mt-1 {
    margin-top: var(--spacing-sm);
}

.mt-2 {
    margin-top: var(--spacing-md);
}

.mb-1 {
    margin-bottom: var(--spacing-sm);
}

.mb-2 {
    margin-bottom: var(--spacing-md);
}

/* Smooth scrolling offset for fixed navbar */
section {
    scroll-margin-top: 80px;
}