/* ====================================
   ELITE DATA SCIENCE PORTFOLIO
   Modern, Minimalist, Recruiter-Optimized
   ==================================== */

/* ====================================
   CSS VARIABLES
   ==================================== */
:root {
    /* Color Palette - High Contrast, Professional */
    --primary-color: #3B82F6;           /* Accent Blue */
    --primary-dark: #2563EB;            /* Darker Blue */
    --primary-light: #60A5FA;           /* Lighter Blue */
    
    --bg-color: #FFFFFF;                /* Pure White */
    --bg-secondary: #F8FAFC;            /* Subtle Gray */
    --bg-tertiary: #F1F5F9;             /* Card Background */
    
    --text-primary: #0F172A;            /* Almost Black */
    --text-secondary: #475569;          /* Medium Gray */
    --text-tertiary: #64748B;           /* Light Gray */
    
    --border-color: #E2E8F0;            /* Subtle Border */
    --border-hover: #CBD5E1;            /* Hover Border */
    
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    
    /* Typography */
    --font-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono: 'SF Mono', 'Monaco', 'Inconsolata', 'Fira Code', monospace;
    
    /* Spacing Scale */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-2xl: 4rem;
    --spacing-3xl: 6rem;
    
    /* Layout */
    --container-max-width: 1200px;
    --content-max-width: 800px;
    --section-padding: 5rem 2rem;
    
    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 250ms ease-in-out;
    --transition-slow: 350ms ease-in-out;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
}

/* ====================================
   RESET & BASE STYLES
   ==================================== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    scroll-behavior: smooth;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: var(--font-primary);
    font-size: 16px;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-color);
    overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
    line-height: 1.2;
    font-weight: 600;
    color: var(--text-primary);
}

h1 { font-size: clamp(2.5rem, 5vw, 4rem); }
h2 { font-size: clamp(2rem, 4vw, 3rem); }
h3 { font-size: clamp(1.25rem, 2.5vw, 1.75rem); }
h4 { font-size: 1.25rem; }
h5 { font-size: 1.125rem; }

p {
    margin-bottom: 1rem;
    color: var(--text-secondary);
}

a {
    color: var(--primary-color);
    text-decoration: none;
    transition: color var(--transition-base);
}

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

ul, ol {
    list-style: none;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

strong {
    font-weight: 600;
    color: var(--text-primary);
}

/* ====================================
   UTILITY CLASSES
   ==================================== */
.container {
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.section {
    padding: var(--section-padding);
}

.section-title {
    font-size: clamp(2rem, 4vw, 2.75rem);
    font-weight: 700;
    margin-bottom: var(--spacing-md);
    text-align: center;
    color: var(--text-primary);
}

.section-subtitle {
    text-align: center;
    font-size: 1.125rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto var(--spacing-xl);
}

/* ====================================
   NAVIGATION
   ==================================== */
.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    box-shadow: var(--shadow-sm);
    z-index: 1000;
    transition: all var(--transition-base);
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem var(--spacing-md);
    max-width: var(--container-max-width);
}

.nav-logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    transition: color var(--transition-base);
}

.nav-logo:hover {
    color: var(--primary-color);
}

.nav-menu {
    display: flex;
    gap: var(--spacing-lg);
    align-items: center;
}

.nav-link {
    font-size: 0.9375rem;
    font-weight: 500;
    color: var(--text-secondary);
    padding: 0.5rem 0;
    position: relative;
    transition: color var(--transition-base);
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background-color: var(--primary-color);
    transition: width var(--transition-base);
}

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

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

.nav-link-cta {
    background-color: var(--primary-color);
    color: white;
    padding: 0.5rem 1.25rem;
    border-radius: var(--radius-md);
}

.nav-link-cta::after {
    display: none;
}

.nav-link-cta:hover {
    background-color: var(--primary-dark);
    color: white;
}

/* ====================================
   HERO SECTION
   ==================================== */
.hero {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--bg-color) 0%, var(--bg-secondary) 100%);
    padding-top: 80px;
}

.hero-container {
    text-align: center;
    max-width: 900px;
}

.hero-content {
    animation: fadeInUp 0.8s ease-out;
}

.hero-name {
    display: block;
    font-size: clamp(3rem, 6vw, 5rem);
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.02em;
}

.hero-subtitle {
    font-size: clamp(1.25rem, 2.5vw, 1.75rem);
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
    line-height: 1.4;
}

.hero-description {
    font-size: clamp(1rem, 2vw, 1.125rem);
    color: var(--text-secondary);
    max-width: 700px;
    margin: 0 auto var(--spacing-xl);
    line-height: 1.7;
}

.hero-cta {
    display: flex;
    gap: var(--spacing-md);
    justify-content: center;
    flex-wrap: wrap;
}

/* ====================================
   BUTTONS
   ==================================== */
.btn {
    display: inline-block;
    padding: 0.875rem 2rem;
    font-size: 1rem;
    font-weight: 600;
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
    cursor: pointer;
    border: 2px solid transparent;
    text-align: center;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
    box-shadow: var(--shadow-md);
}

.btn-primary:hover {
    background-color: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
    color: white;
}

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

.btn-secondary:hover {
    background-color: var(--text-secondary);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
    color: white;
}

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

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

/* ====================================
   ABOUT SECTION
   ==================================== */
.about {
    background-color: var(--bg-color);
}

.about-content {
    max-width: var(--content-max-width);
    margin: 0 auto;
}

.about-text p {
    font-size: 1.125rem;
    line-height: 1.8;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

.about-text p:last-child {
    margin-bottom: 0;
}

/* ====================================
   SKILLS SECTION
   ==================================== */
.skills {
    background-color: var(--bg-secondary);
}

.skills-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-lg);
    max-width: var(--container-max-width);
    margin: 0 auto;
}

.skill-category {
    background-color: var(--bg-color);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

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

.skill-category-title {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.skill-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
}

.skill-tag {
    display: inline-block;
    padding: 0.5rem 1rem;
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
    font-size: 0.875rem;
    font-weight: 500;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.skill-tag:hover {
    background-color: var(--primary-color);
    color: white;
    transform: scale(1.05);
}

/* ====================================
   EXPERIENCE SECTION
   ==================================== */
.experience {
    background-color: var(--bg-color);
}

.timeline {
    max-width: 900px;
    margin: 0 auto;
    position: relative;
    padding-left: var(--spacing-lg);
}

.timeline::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 2px;
    background-color: var(--border-color);
}

.timeline-item {
    position: relative;
    padding-bottom: var(--spacing-xl);
}

.timeline-item:last-child {
    padding-bottom: 0;
}

.timeline-marker {
    position: absolute;
    left: -31px;
    top: 8px;
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background-color: var(--primary-color);
    border: 3px solid var(--bg-color);
    box-shadow: 0 0 0 2px var(--primary-color);
}

.timeline-content {
    background-color: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

.timeline-content:hover {
    box-shadow: var(--shadow-md);
    transform: translateX(4px);
}

.timeline-header {
    margin-bottom: var(--spacing-md);
}

.timeline-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.timeline-company {
    display: block;
    font-size: 1.125rem;
    font-weight: 500;
    color: var(--primary-color);
    margin-bottom: var(--spacing-xs);
}

.timeline-period {
    display: inline-block;
    font-size: 0.9375rem;
    color: var(--text-tertiary);
    padding: 0.25rem 0.75rem;
    background-color: var(--bg-tertiary);
    border-radius: var(--radius-sm);
}

.timeline-description {
    list-style: none;
}

.timeline-description li {
    position: relative;
    padding-left: 1.5rem;
    margin-bottom: var(--spacing-sm);
    color: var(--text-secondary);
    line-height: 1.7;
}

.timeline-description li::before {
    content: '▸';
    position: absolute;
    left: 0;
    color: var(--primary-color);
    font-weight: 700;
}

.timeline-description li:last-child {
    margin-bottom: 0;
}

/* ====================================
   PROJECTS SECTION
   ==================================== */
.projects {
    background-color: var(--bg-secondary);
}

.projects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: var(--spacing-xl);
    max-width: var(--container-max-width);
    margin: 0 auto;
}

.project-card {
    background-color: var(--bg-color);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
    display: flex;
    flex-direction: column;
    height: 100%;
}

.project-card:hover {
    box-shadow: var(--shadow-xl);
    transform: translateY(-8px);
}

.project-header {
    margin-bottom: var(--spacing-md);
}

.project-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-sm);
    line-height: 1.3;
}

.project-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
    margin-top: var(--spacing-sm);
}

.project-tag {
    font-size: 0.75rem;
    font-weight: 600;
    padding: 0.375rem 0.75rem;
    background-color: var(--primary-light);
    color: white;
    border-radius: var(--radius-sm);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.project-body {
    flex-grow: 1;
    margin-bottom: var(--spacing-md);
}

.project-body p {
    font-size: 0.9375rem;
    line-height: 1.7;
    margin-bottom: var(--spacing-sm);
    color: var(--text-secondary);
}

.project-body p:last-child {
    margin-bottom: 0;
}

.project-footer {
    padding-top: var(--spacing-md);
    border-top: 1px solid var(--border-color);
}

.project-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 600;
    color: var(--primary-color);
    transition: all var(--transition-base);
}

.project-link:hover {
    color: var(--primary-dark);
    gap: 0.75rem;
}

.project-link .icon {
    transition: transform var(--transition-base);
}

.project-link:hover .icon {
    transform: translateX(2px);
}

/* ====================================
   RESEARCH SECTION
   ==================================== */
.research {
    background-color: var(--bg-color);
}

.publications-list {
    max-width: 900px;
    margin: 0 auto;
}

.publication-item {
    background-color: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    margin-bottom: var(--spacing-lg);
    transition: all var(--transition-base);
    border-left: 4px solid var(--primary-color);
}

.publication-item:last-child {
    margin-bottom: 0;
}

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

.publication-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
    line-height: 1.4;
}

.publication-authors {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-xs);
}

.publication-venue {
    font-size: 0.9375rem;
    color: var(--text-tertiary);
    font-style: italic;
    margin-bottom: var(--spacing-sm);
}

.publication-summary {
    font-size: 1rem;
    line-height: 1.7;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

.publication-links {
    display: flex;
    gap: var(--spacing-md);
    flex-wrap: wrap;
}

.publication-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.875rem;
    font-weight: 600;
    padding: 0.5rem 1rem;
    background-color: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--primary-color);
    transition: all var(--transition-base);
}

.publication-link:hover {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
    color: white;
    transform: translateY(-2px);
}

/* ====================================
   EDUCATION SECTION
   ==================================== */
.education {
    background-color: var(--bg-secondary);
}

.education-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    max-width: 900px;
    margin: 0 auto var(--spacing-xl);
}

.education-item {
    display: flex;
    gap: var(--spacing-md);
    background-color: var(--bg-color);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

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

.education-icon {
    flex-shrink: 0;
    width: 48px;
    height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: var(--primary-color);
    color: white;
    border-radius: var(--radius-md);
}

.education-content {
    flex-grow: 1;
}

.education-degree {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-xs);
}

.education-school {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 0.25rem;
}

.education-period {
    font-size: 0.875rem;
    color: var(--text-tertiary);
    display: block;
    margin-bottom: var(--spacing-xs);
}

.education-details {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

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

.certifications-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: var(--spacing-md);
    text-align: center;
}

.certifications-list {
    display: grid;
    gap: var(--spacing-md);
}

.cert-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-md);
    background-color: var(--bg-color);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
    flex-wrap: wrap;
    gap: var(--spacing-sm);
}

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

.cert-item strong {
    color: var(--text-primary);
    font-weight: 600;
}

.cert-item span {
    color: var(--text-tertiary);
    font-size: 0.9375rem;
}

/* ====================================
   CONTACT SECTION
   ==================================== */
.contact {
    background-color: var(--bg-color);
}

.contact-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
    max-width: 900px;
    margin: 0 auto var(--spacing-xl);
}

.contact-card {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-lg);
    background-color: var(--bg-secondary);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
    border: 2px solid transparent;
}

.contact-card:hover {
    box-shadow: var(--shadow-md);
    transform: translateY(-4px);
    border-color: var(--primary-color);
}

.contact-icon {
    flex-shrink: 0;
    width: 56px;
    height: 56px;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: var(--primary-color);
    color: white;
    border-radius: var(--radius-md);
}

.contact-content h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.25rem;
}

.contact-content p {
    font-size: 0.9375rem;
    color: var(--text-secondary);
    margin: 0;
    word-break: break-word;
}

.contact-cta {
    text-align: center;
    max-width: 600px;
    margin: 0 auto;
}

.contact-cta p {
    font-size: 1.125rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

/* ====================================
   FOOTER
   ==================================== */
.footer {
    background-color: var(--text-primary);
    color: white;
    padding: var(--spacing-xl) var(--spacing-md);
    text-align: center;
}

.footer-container {
    max-width: var(--container-max-width);
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.footer-text {
    color: rgba(255, 255, 255, 0.8);
    margin: 0;
}

.footer-links {
    display: flex;
    gap: var(--spacing-md);
}

.footer-link {
    color: rgba(255, 255, 255, 0.8);
    font-weight: 500;
    transition: color var(--transition-base);
}

.footer-link:hover {
    color: white;
}

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

@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

/* Scroll Animation Class */
.fade-in-section {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s ease-out, transform 0.6s ease-out;
}

.fade-in-section.is-visible {
    opacity: 1;
    transform: translateY(0);
}

/* ====================================
   RESPONSIVE DESIGN
   ==================================== */

/* Tablets */
@media (max-width: 768px) {
    :root {
        --section-padding: 3rem 1.5rem;
    }
    
    .nav-menu {
        gap: var(--spacing-md);
    }
    
    .nav-link {
        font-size: 0.875rem;
    }
    
    .hero-cta {
        flex-direction: column;
        align-items: center;
    }
    
    .btn {
        width: 100%;
        max-width: 300px;
    }
    
    .timeline {
        padding-left: var(--spacing-md);
    }
    
    .timeline-marker {
        left: -25px;
    }
    
    .projects-grid {
        grid-template-columns: 1fr;
    }
    
    .skills-grid {
        grid-template-columns: 1fr;
    }
    
    .education-grid {
        grid-template-columns: 1fr;
    }
    
    .contact-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-container {
        flex-direction: column;
        text-align: center;
    }
}

/* Mobile */
@media (max-width: 480px) {
    :root {
        --section-padding: 2rem 1rem;
    }
    
    .nav-container {
        flex-direction: column;
        gap: var(--spacing-sm);
        padding: 0.75rem 1rem;
    }
    
    .nav-menu {
        flex-wrap: wrap;
        justify-content: center;
        gap: var(--spacing-sm);
    }
    
    .hero {
        min-height: 90vh;
    }
    
    .section-title {
        margin-bottom: var(--spacing-md);
    }
    
    .timeline-content {
        padding: var(--spacing-md);
    }
    
    .timeline-title {
        font-size: 1.25rem;
    }
    
    .project-card {
        padding: var(--spacing-md);
    }
    
    .cert-item {
        flex-direction: column;
        align-items: flex-start;
        text-align: left;
    }
}

/* ====================================
   PRINT STYLES
   ==================================== */
@media print {
    .nav, .footer, .hero-cta, .btn {
        display: none;
    }
    
    .section {
        padding: 1rem 0;
        page-break-inside: avoid;
    }
    
    body {
        font-size: 12pt;
        line-height: 1.5;
        color: black;
    }
    
    a {
        color: black;
        text-decoration: underline;
    }
}

/* ====================================
   ACCESSIBILITY
   ==================================== */
.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
}

/* Focus Styles */
a:focus,
button:focus,
input:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* High Contrast Mode Support */
@media (prefers-contrast: high) {
    :root {
        --text-secondary: var(--text-primary);
        --border-color: var(--text-primary);
    }
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}