/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', sans-serif;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-primary);
    transition: background-color 0.3s ease, color 0.3s ease;
}

/* CSS Variables for Light/Dark Theme */
:root {
    --bg-primary: #ffffff;
    --bg-primary-rgb: 255, 255, 255;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --accent-primary: #3b82f6;
    --accent-secondary: #1d4ed8;
    --border-color: #e2e8f0;
    --shadow-light: rgba(0, 0, 0, 0.05);
    --shadow-medium: rgba(0, 0, 0, 0.1);
    --shadow-strong: rgba(0, 0, 0, 0.15);
}

[data-theme="dark"] {
    --bg-primary: #0f172a;
    --bg-primary-rgb: 15, 23, 42;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --text-primary: #f8fafc;
    --text-secondary: #cbd5e1;
    --text-muted: #94a3b8;
    --accent-primary: #60a5fa;
    --accent-secondary: #3b82f6;
    --border-color: #334155;
    --shadow-light: rgba(0, 0, 0, 0.2);
    --shadow-medium: rgba(0, 0, 0, 0.3);
    --shadow-strong: rgba(0, 0, 0, 0.4);
}

/* Container */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
}

/* Experience Timeline */
.timeline {
    position: relative;
    max-width: 1000px;
    margin: 0 auto;
    padding: 3rem 0;
}

/* Navigation */
.navbar {
    position: fixed;
    top: 0;
    width: 100%;
    background: var(--bg-primary);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    z-index: 1000;
    transition: all 0.3s ease;
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 2rem;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 70px;
    position: relative;
}

.nav-logo {
    position: absolute;
    left: 2rem;
}

.nav-logo a {
    font-size: 1.8rem;
    font-weight: 800;
    color: var(--primary-color);
    text-decoration: none;
    transition: color 0.3s ease;
    font-family: 'Inter', sans-serif;
    letter-spacing: -0.02em;
}

.nav-menu {
    display: flex;
    list-style: none;
    margin: 0;
    padding: 0;
    gap: 2rem;
    justify-content: center;
    flex: 1;
}

.nav-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s ease;
    position: relative;
    width: 100%;
}

.nav-link:hover,
.nav-link.active {
    color: var(--accent-primary);
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: -5px;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--accent-primary);
    transition: width 0.3s ease;
}

.nav-link:hover::after,
.nav-link.active::after {
    width: 100%;
}

.theme-toggle {
    background: none;
    border: 2px solid var(--border-color);
    color: var(--text-primary);
    padding: 0.5rem;
    border-radius: 50%;
    cursor: pointer;
    transition: all 0.3s ease;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    position: absolute;
    right: 2rem;
}

.hamburger {
    display: none;
    flex-direction: column;
    cursor: pointer;
}

.bar {
    width: 25px;
    height: 3px;
    background: var(--text-primary);
    margin: 3px 0;
    transition: 0.3s;
}

/* Hero Section */
.hero {
    padding: 120px 0 80px;
    min-height: 100vh;
    display: flex;
    align-items: center;
    background: linear-gradient(135deg, var(--bg-primary) 0%, var(--bg-secondary) 100%);
}

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

.hero-title {
    font-size: 3.5rem;
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--text-primary);
    line-height: 1.2;
}

.highlight {
    color: var(--accent-primary);
}

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

.hero-description {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 2.5rem;
    line-height: 1.7;
    max-width: 600px;
}

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

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.5rem;
    border-radius: 0.5rem;
    text-decoration: none;
    font-weight: 500;
    transition: all 0.3s ease;
    border: none;
    cursor: pointer;
    font-size: 1rem;
}

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

.btn-primary:hover {
    background: var(--accent-secondary);
    transform: translateY(-2px);
    box-shadow: 0 10px 25px var(--shadow-medium);
}

.btn-secondary {
    background: transparent;
    color: var(--text-primary);
    border: 2px solid var(--border-color);
}

.btn-secondary:hover {
    background: var(--bg-secondary);
    transform: translateY(-2px);
    box-shadow: 0 10px 25px var(--shadow-light);
}

/* Sections */
section {
    padding: 80px 0;
}

.section-title {
    font-size: 2.5rem;
    font-weight: 700;
    text-align: center;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.section-subtitle {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 3rem;
    font-size: 1.1rem;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

/* About Section */
.about {
    background: var(--bg-secondary);
}

.about-text {
    max-width: 800px;
    margin: 0 auto;
    text-align: center;
}

.about-text p {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    line-height: 1.7;
}

/* Experience Timeline */
.experience {
    background: var(--bg-primary);
}

.timeline {
    max-width: 1000px;
    margin: 0 auto;
    position: relative;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 200px;
    width: 2px;
    height: 100%;
    background: var(--border-color);
}

.timeline-item {
    display: flex;
    align-items: flex-start;
    position: relative;
    margin: 60px 0;
    width: 100%;
}

.timeline-dot {
    height: 16px;
    width: 16px;
    background: var(--accent-primary);
    border-radius: 50%;
    position: absolute;
    top: 8px;
    left: 192px;
    z-index: 1;
    border: 3px solid var(--bg-primary);
}

.timeline-date {
    width: 180px;
    text-align: right;
    padding-right: 30px;
    flex-shrink: 0;
}

.date-text {
    font-size: 0.9rem;
    color: var(--text-muted);
    font-weight: 600;
    line-height: 1.4;
}

.timeline-content {
    background: var(--bg-secondary);
    padding: 2rem;
    border-radius: 0.75rem;
    border: 1px solid var(--border-color);
    flex: 1;
    margin-left: 30px;
}

.timeline-content h3 {
    color: var(--text-primary);
    font-size: 1.3rem;
    margin-bottom: 0.25rem;
}

.timeline-content h4 {
    color: var(--accent-primary);
    font-size: 1.1rem;
    margin-bottom: 1rem;
    font-weight: 600;
}

.timeline-content ul {
    margin: 0;
    padding-left: 1.2rem;
}

.timeline-content li {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 0.5rem;
}

/* Resume Download Section */
.resume-download {
    text-align: center;
    margin-top: 3rem;
    padding: 2rem;
    background: var(--bg-secondary);
    border-radius: 0.75rem;
    border: 1px solid var(--border-color);
}

.resume-text {
    font-size: 1.1rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    font-weight: 500;
}

.resume-btn {
    font-size: 1rem;
    padding: 0.875rem 2rem;
}

.resume-btn i {
    margin-right: 0.5rem;
}

/* Skills Section */
.skills {
    background: var(--bg-secondary);
}

.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 2rem;
    max-width: 1000px;
    margin: 0 auto;
}

.skill-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 2rem 1rem;
    background: var(--bg-primary);
    border-radius: 0.75rem;
    box-shadow: 0 4px 15px var(--shadow-light);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
}

.skill-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 10px 30px var(--shadow-medium);
}

.skill-icon {
    font-size: 3rem;
    color: var(--accent-primary);
    margin-bottom: 1rem;
}

.skill-name {
    font-weight: 600;
    color: var(--text-primary);
    text-align: center;
}

/* Projects Section */
.projects {
    background: var(--bg-primary);
}

.projects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 2rem;
    max-width: 1200px;
    margin: 0 auto;
}

.project-card {
    background: var(--bg-secondary);
    border-radius: 0.75rem;
    padding: 2rem;
    box-shadow: 0 4px 15px var(--shadow-light);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
}

.project-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 15px 40px var(--shadow-medium);
}

.project-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.project-header h3 {
    color: var(--text-primary);
    font-size: 1.3rem;
    font-weight: 600;
}

.project-links {
    display: flex;
    gap: 0.5rem;
}

.project-link {
    color: var(--text-secondary);
    font-size: 1.2rem;
    transition: color 0.3s ease;
}

.project-link:hover {
    color: var(--accent-primary);
}

.project-description {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 1.5rem;
}

.project-tech {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.tech-tag {
    background: var(--accent-primary);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 1rem;
    font-size: 0.85rem;
    font-weight: 500;
}

/* Publications Section */
.publications {
    background: var(--bg-primary);
}

.publication-card {
    max-width: 800px;
    margin: 0 auto;
    background: var(--bg-secondary);
    border-radius: 0.75rem;
    padding: 2rem;
    box-shadow: 0 4px 15px var(--shadow-light);
    border: 1px solid var(--border-color);
}

.publication-title {
    color: var(--text-primary);
    font-size: 1.4rem;
    font-weight: 600;
    margin-bottom: 1rem;
    line-height: 1.4;
}

.publication-authors {
    color: var(--text-secondary);
    font-size: 1rem;
    margin-bottom: 0.5rem;
    font-style: italic;
}

.publication-meta {
    display: flex;
    gap: 1rem;
    margin-bottom: 1rem;
    flex-wrap: wrap;
}

.publication-meta span {
    color: var(--accent-primary);
    font-size: 0.9rem;
    font-weight: 500;
}

.publication-description {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 1.5rem;
}

.publication-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--accent-primary);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s ease;
}

.publication-link:hover {
    color: var(--accent-secondary);
}

/* Contact Section */
.contact {
    background: var(--bg-secondary);
}

.contact-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    max-width: 1000px;
    margin: 0 auto;
}

.contact-info {
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

.contact-item {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.contact-item i {
    font-size: 1.5rem;
    color: var(--accent-primary);
    width: 2rem;
}

.contact-item h4 {
    color: var(--text-primary);
    margin-bottom: 0.25rem;
    font-weight: 600;
}

.contact-item p {
    color: var(--text-secondary);
}

.social-links {
    display: flex;
    gap: 1rem;
    margin-top: 1rem;
}

.social-links a {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 3rem;
    height: 3rem;
    background: var(--bg-primary);
    color: var(--text-secondary);
    border-radius: 50%;
    font-size: 1.2rem;
    transition: all 0.3s ease;
    border: 1px solid var(--border-color);
}

.social-links a:hover {
    background: var(--accent-primary);
    color: white;
    transform: translateY(-2px);
}

.contact-form {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.form-group {
    display: flex;
    flex-direction: column;
}

.form-group input,
.form-group textarea {
    padding: 1rem;
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    background: var(--bg-primary);
    color: var(--text-primary);
    font-size: 1rem;
    transition: all 0.3s ease;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.form-group textarea {
    resize: vertical;
    min-height: 120px;
}

/* Footer */
.footer {
    background: var(--bg-primary);
    border-top: 1px solid var(--border-color);
    padding: 2rem 0;
    text-align: center;
}

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

/* Responsive Design */
@media (max-width: 768px) {
    .nav-container {
        padding: 0 1rem;
    }
    
    .nav-logo {
        left: 1rem;
    }
    
    .theme-toggle {
        right: 4rem;
    }
    
    .nav-menu {
        position: fixed;
        left: -100%;
        top: 70px;
        flex-direction: column;
        background: var(--bg-primary);
        width: 100%;
        text-align: center;
        transition: 0.3s;
        box-shadow: 0 10px 27px rgba(0, 0, 0, 0.05);
        border-bottom: 1px solid var(--border-color);
        padding: 2rem 0;
        gap: 0;
        justify-content: flex-start;
    }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .hero-subtitle {
        font-size: 1.2rem;
    }
    
    .hero-buttons {
        flex-direction: column;
        align-items: center;
    }
    
    .timeline::before {
        left: 20px;
    }
    
    .timeline-item {
        flex-direction: column;
        align-items: flex-start;
        padding-left: 50px;
    }
    
    .timeline-date {
        width: auto;
        text-align: left;
        padding-right: 0;
        margin-bottom: 1rem;
    }
    
    .timeline-content {
        margin-left: 0;
    }
    
    .timeline-dot {
        left: 10px !important;
    }
    
    .skills-grid {
        grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
        gap: 1rem;
    }
    
    .projects-grid {
        grid-template-columns: 1fr;
    }
    
    .contact-content {
        grid-template-columns: 1fr;
        gap: 2rem;
    }
    
    .container {
        padding: 0 1rem;
    }
    
    .nav-container {
        padding: 0 1rem;
    }
    
    .hamburger {
        display: block;
        cursor: pointer;
        position: absolute;
        right: 1rem;
    }
}

@media (max-width: 480px) {
    .hero-title {
        font-size: 2rem;
    }
    
    .section-title {
        font-size: 2rem;
    }
    
    .skill-item {
        padding: 1.5rem 0.5rem;
    }
    
    .project-card {
        padding: 1.5rem;
    }
}

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

.fade-in-up {
    animation: fadeInUp 0.6s ease-out;
}

/* Scroll animations will be handled by JavaScript */
.animate-on-scroll {
    opacity: 0;
    transform: translateY(30px);
    transition: all 0.6s ease-out;
}

.animate-on-scroll.animated {
    opacity: 1;
    transform: translateY(0);
}