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

:root {
    /* Color Palette - Light, Professional Theme */
    --primary-color: #2c5282;
    --secondary-color: #4299e1;
    --accent-color: #3182ce;
    --text-primary: #2d3748;
    --text-secondary: #4a5568;
    --text-light: #5a6678; /* Updated from #718096 for better contrast (4.5:1 ratio) */
    --background: #ffffff;
    --background-alt: #f7fafc;
    --background-section: #edf2f7;
    --border-color: #e2e8f0;
    --hover-color: #2b6cb0;

    /* Typography */
    --font-primary: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    --font-secondary: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-xxl: 4rem;

    /* Transitions */
    --transition-speed: 0.3s;
}

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

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

/* ===========================
   Navigation Bar
   =========================== */
.navbar {
    position: sticky;
    top: 0;
    background-color: var(--background);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
    z-index: 1000;
    padding: var(--spacing-sm) 0;
}

.nav-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.nav-brand {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-color);
    text-decoration: none;
    transition: color var(--transition-speed);
}

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

.nav-links {
    display: flex;
    list-style: none;
    gap: var(--spacing-lg);
}

.nav-links a {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    transition: color var(--transition-speed), border-bottom-color var(--transition-speed);
    padding: var(--spacing-xs) 0;
    border-bottom: 2px solid transparent;
}

.nav-links a:hover,
.nav-links a:focus {
    color: var(--primary-color);
    border-bottom-color: var(--secondary-color);
}

/* Active navigation link state */
.nav-links a.active {
    color: var(--primary-color);
    border-bottom-color: var(--secondary-color);
    font-weight: 600;
}

/* Mobile Navigation */
@media (max-width: 768px) {
    .nav-container {
        flex-direction: column;
        gap: var(--spacing-sm);
    }

    .nav-links {
        flex-wrap: wrap;
        gap: var(--spacing-sm);
        justify-content: center;
    }

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

/* ===========================
   Container & Layout
   =========================== */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

section {
    padding: var(--spacing-xxl) 0;
}

/* ===========================
   Hero Section
   =========================== */
.hero-section {
    background: linear-gradient(135deg, var(--background-alt) 0%, var(--background-section) 100%);
    padding: var(--spacing-xl) 0;
}

.hero-content {
    display: grid;
    grid-template-columns: 250px 1fr;
    gap: var(--spacing-xl);
    align-items: center;
}

.hero-image img {
    width: 100%;
    height: auto;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.hero-text h1 {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: var(--spacing-sm);
    font-weight: 700;
}

.tagline {
    font-size: 1.2rem;
    color: var(--text-secondary);
    line-height: 1.7;
    margin-bottom: var(--spacing-lg);
}

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

/* Mobile Hero */
@media (max-width: 768px) {
    .hero-content {
        grid-template-columns: 1fr;
        gap: var(--spacing-md);
        text-align: center;
    }

    .hero-image {
        max-width: 200px;
        margin: 0 auto;
    }

    .hero-text h1 {
        font-size: 2rem;
    }

    .tagline {
        font-size: 1.1rem;
    }

    .hero-links {
        justify-content: center;
    }
}

/* ===========================
   Buttons
   =========================== */
.btn {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    transition: all var(--transition-speed);
    cursor: pointer;
    border: none;
    font-size: 1rem;
}

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

.btn-primary:hover,
.btn-primary:focus {
    background-color: var(--hover-color);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(44, 82, 130, 0.3);
}

.btn-primary:disabled {
    background-color: #cbd5e0;
    cursor: not-allowed;
    transform: none;
}

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

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

.btn-research {
    background-color: var(--secondary-color);
    color: white;
    padding: 0.6rem 1.2rem;
}

.btn-research:hover,
.btn-research:focus {
    background-color: var(--hover-color);
    transform: translateY(-2px);
}

/* ===========================
   Typography
   =========================== */
h2 {
    font-size: 2.25rem;
    color: var(--primary-color);
    margin-bottom: var(--spacing-lg);
    font-weight: 700;
    border-bottom: 3px solid var(--secondary-color);
    padding-bottom: var(--spacing-sm);
}

h3 {
    font-size: 1.5rem;
    color: var(--primary-color);
    margin-bottom: var(--spacing-sm);
    font-weight: 600;
}

h4 {
    font-size: 1.25rem;
    color: var(--text-primary);
    font-weight: 600;
}

/* ===========================
   Experience Section
   =========================== */
.experience-section {
    background-color: var(--background);
}

.experience-category {
    margin-bottom: var(--spacing-xl);
    padding: var(--spacing-lg);
    background-color: var(--background-alt);
    border-radius: 12px;
    border-left: 4px solid var(--secondary-color);
}

.category-header {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.category-icon {
    color: var(--primary-color);
    flex-shrink: 0;
}

.job {
    background-color: var(--background);
    padding: var(--spacing-md);
    border-radius: 8px;
    margin-bottom: var(--spacing-md);
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.05);
    transition: transform var(--transition-speed), box-shadow var(--transition-speed);
}

.job:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.job-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: var(--spacing-sm);
    gap: var(--spacing-md);
}

.company {
    color: var(--secondary-color);
    font-weight: 600;
    font-size: 1.05rem;
    margin-top: 0.25rem;
}

.date {
    color: var(--text-light);
    font-style: italic;
    white-space: nowrap;
}

.job-description {
    list-style-position: outside;
    margin-left: var(--spacing-md);
    color: var(--text-secondary);
}

.job-description li {
    margin-bottom: var(--spacing-xs);
    line-height: 1.6;
}

/* Mobile Experience */
@media (max-width: 768px) {
    .category-header {
        flex-direction: column;
        text-align: center;
    }

    .job-header {
        flex-direction: column;
        gap: var(--spacing-xs);
    }

    .date {
        white-space: normal;
    }
}

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

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

.education-card {
    background-color: var(--background);
    padding: var(--spacing-lg);
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    text-align: center;
    transition: transform var(--transition-speed), box-shadow var(--transition-speed);
}

.education-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.12);
}

.degree-icon {
    color: var(--secondary-color);
    margin-bottom: var(--spacing-sm);
}

.institution {
    color: var(--text-secondary);
    font-weight: 600;
    font-size: 1.1rem;
    margin-top: var(--spacing-xs);
}

.year {
    color: var(--text-light);
    font-style: italic;
    margin-top: var(--spacing-xs);
}

.dissertation {
    color: var(--text-secondary);
    font-size: 0.95rem;
    margin-top: var(--spacing-sm);
    line-height: 1.5;
}

.awards-section {
    background-color: var(--background);
    padding: var(--spacing-lg);
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
}

.awards-section h3 {
    margin-bottom: var(--spacing-md);
}

.awards-list {
    list-style: none;
}

.awards-list li {
    margin-bottom: var(--spacing-md);
    padding-left: var(--spacing-md);
    border-left: 3px solid var(--secondary-color);
}

.awards-list strong {
    color: var(--primary-color);
    display: block;
    margin-bottom: var(--spacing-xs);
}

.awards-list p {
    color: var(--text-secondary);
    line-height: 1.6;
}

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

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

.research-card {
    background-color: var(--background-alt);
    padding: var(--spacing-lg);
    border-radius: 12px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
    display: flex;
    flex-direction: column;
    transition: transform var(--transition-speed), box-shadow var(--transition-speed);
}

.research-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.12);
}

.research-card h3 {
    color: var(--primary-color);
    margin-bottom: var(--spacing-sm);
}

.research-description {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: var(--spacing-md);
    flex-grow: 1;
}

/* ===========================
   Contact Page
   =========================== */
.contact-section {
    background: linear-gradient(135deg, var(--background-alt) 0%, var(--background-section) 100%);
    min-height: calc(100vh - 200px);
    display: flex;
    align-items: center;
}

.contact-container {
    max-width: 600px;
    margin: 0 auto;
    padding: var(--spacing-xl);
}

.contact-intro {
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

.contact-intro h1 {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: var(--spacing-sm);
}

.contact-intro p {
    font-size: 1.1rem;
    color: var(--text-secondary);
}

.contact-form {
    background-color: var(--background);
    padding: var(--spacing-xl);
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.form-group {
    margin-bottom: var(--spacing-md);
}

.form-group label {
    display: block;
    color: var(--text-primary);
    font-weight: 600;
    margin-bottom: var(--spacing-xs);
}

.form-group input,
.form-group textarea {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-family: inherit;
    font-size: 1rem;
    transition: border-color var(--transition-speed);
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--secondary-color);
}

.form-group textarea {
    min-height: 150px;
    resize: vertical;
}

.form-error {
    color: #e53e3e;
    font-size: 0.9rem;
    margin-top: var(--spacing-xs);
    display: none;
}

.form-group.error input,
.form-group.error textarea {
    border-color: #e53e3e;
}

.form-group.error .form-error {
    display: block;
}

.form-actions {
    display: flex;
    gap: var(--spacing-md);
    justify-content: flex-end;
}

.form-message {
    padding: var(--spacing-md);
    border-radius: 8px;
    margin-bottom: var(--spacing-md);
    display: none;
}

.form-message.success {
    background-color: #c6f6d5;
    color: #22543d;
    border: 1px solid #9ae6b4;
}

.form-message.error {
    background-color: #fed7d7;
    color: #742a2a;
    border: 1px solid #fc8181;
}

/* ===========================
   PDF Viewer Pages
   =========================== */
.pdf-section {
    background-color: var(--background-section);
    min-height: calc(100vh - 100px);
    padding: var(--spacing-lg) 0;
}

.pdf-container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

.pdf-header {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.pdf-header h1 {
    font-size: 2rem;
    color: var(--primary-color);
    margin-bottom: var(--spacing-sm);
}

.back-link {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    color: var(--secondary-color);
    text-decoration: none;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    transition: color var(--transition-speed);
}

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

.pdf-viewer {
    background-color: var(--background);
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    overflow: hidden;
}

.pdf-viewer embed {
    width: 100%;
    height: 800px;
    border: none;
}

/* PDF download link styling */
.pdf-download-link {
    text-align: center;
    padding: 20px;
}

/* ===========================
   Footer
   =========================== */
.footer {
    background-color: var(--primary-color);
    color: white;
    padding: var(--spacing-lg) 0;
    text-align: center;
}

.footer a {
    color: white;
    text-decoration: none;
    transition: opacity var(--transition-speed);
}

.footer a:hover,
.footer a:focus {
    opacity: 0.8;
    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 for keyboard navigation */
a:focus-visible,
button:focus-visible,
input:focus-visible,
textarea:focus-visible {
    outline: 3px solid var(--secondary-color);
    outline-offset: 2px;
}

/* ===========================
   Responsive Design
   =========================== */
@media (max-width: 1024px) {
    :root {
        font-size: 15px;
    }

    .container {
        padding: 0 var(--spacing-sm);
    }
}

@media (max-width: 768px) {
    section {
        padding: var(--spacing-lg) 0;
    }

    h2 {
        font-size: 1.75rem;
    }

    .research-grid,
    .education-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    :root {
        font-size: 14px;
    }

    .btn {
        padding: 0.6rem 1.2rem;
        font-size: 0.95rem;
    }
}