/* --- VARIABLES --- */
     :root {
    /* --- LIGHT THEME PALETTE --- */

    /* Backgrounds */
    --color-background: #f7f9fc;
    --color-background-light: #ffffff;
    --color-background-alt: #f0f4fa;
    --color-surface: #ffffff;

    /* Text */
    --color-text: #1a1f2b;
    --color-text-secondary: #4a5568;
    --color-text-tertiary: #2d3748;

    /* Primary / Secondary Colors */
    --color-primary: #1a73e8; /* Light Blue / Academic vibe */
    --color-primary-light: #e3edfc;
    --color-secondary: #3366cc;
    --color-secondary-transparent: rgba(51, 102, 204, 0.1);

    /* Accent (for highlights, overlines, icons, hovers) */
    --color-accent: #7b4ae2;

    /* Borders */
    --color-border: #d1d9e6;

    /* Typography */
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-serif: 'Playfair Display', Georgia, serif;

    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 2rem;
    --spacing-lg: 4rem;
    --spacing-xl: 8rem;

    /* Radii */
    --border-radius-sm: 4px;
    --border-radius-md: 8px;
    --border-radius-lg: 16px;
    --border-radius-full: 9999px;

    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-medium: 0.3s ease;
    --transition-slow: 0.5s ease;

    /* Shadows (adjusted for light mode) */
    --shadow-small: 0 2px 10px rgba(0, 0, 0, 0.06);
    --shadow-medium: 0 4px 20px rgba(0, 0, 0, 0.08);
    --shadow-large: 0 10px 40px rgba(0, 0, 0, 0.1);
}
    
    /* --- RESET & BASE STYLES --- */
    *, *::before, *::after {
        box-sizing: border-box;
        margin: 0;
        padding: 0;
    }
    
    html {
        font-size: 16px;
        scroll-behavior: smooth;
    }
    
    body {
        font-family: var(--font-sans);
        font-weight: 400;
        line-height: 1.6;
        color: var(--color-text-secondary);
        background-color: var(--color-background);
        -webkit-font-smoothing: antialiased;
        -moz-osx-font-smoothing: grayscale;
    }
    
    img {
        max-width: 100%;
        height: auto;
        display: block;
    }
    
    a {
        color: var(--color-secondary);
        text-decoration: none;
        transition: var(--transition-fast);
    }
    
    a:hover {
        color: var(--color-accent);
    }
    
    ul {
        list-style: none;
    }
    
    /* --- LAYOUT --- */
    .container {
        width: 100%;
        max-width: 1200px;
        margin: 0 auto;
        padding: 0 var(--spacing-md);
    }
    
    .section {
        padding: var(--spacing-xl) 0;
        position: relative;
    }
    
    .accent-bg {
        background-color: var(--color-background-light);
    }
    
    .accent-bg-alt {
        background-color: var(--color-background-alt);
    }
    
    /* --- TYPOGRAPHY --- */
    h1, h2, h3, h4, h5, h6 {
        font-family: var(--font-serif);
        margin-bottom: var(--spacing-sm);
        color: var(--color-text-tertiary);
        line-height: 1.3;
        font-weight: 700;
    }
    
    h1 {
        font-size: 4rem;
        letter-spacing: -1px;
    }
    
    h2 {
        font-size: 2.5rem;
        letter-spacing: -0.5px;
    }
    
    h3 {
        font-size: 1.75rem;
    }
    
    p {
        margin-bottom: var(--spacing-sm);
    }
    
    .lead {
        font-size: 1.25rem;
        margin-bottom: var(--spacing-md);
        color: var(--color-text-secondary);
    }
    
    .highlight {
        color: var(--color-secondary);
    }
    
    .overline {
        font-family: var(--font-sans);
        font-size: 0.875rem;
        font-weight: 600;
        text-transform: uppercase;
        letter-spacing: 2px;
        color: var(--color-accent);
        margin-bottom: var(--spacing-xs);
        display: block;
    }
    
    /* --- HEADER & NAVIGATION --- */
    header {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        z-index: 100;
        transition: var(--transition-medium);
        padding: var(--spacing-sm) 0;

        background-color: rgba(255, 255, 255, 0.8);
        backdrop-filter: blur(10px);
        border-bottom: 1px solid var(--color-border);
    }
    
    .header-container {
        display: flex;
        justify-content: space-between;
        align-items: center;
        max-width: 1200px;
        margin: 0 auto;
        padding: 0 var(--spacing-md);
    }
    
    .logo a {
        font-family: var(--font-serif);
        font-size: 1.5rem;
        font-weight: 700;
        color: var(--color-secondary);
        display: block;
        text-decoration: none;
    }
    
    .main-nav {
        display: flex;
        align-items: center;
    }
    
    .nav-menu {
        display: flex;
        gap: var(--spacing-md);
    }
    
    .nav-link {
        color: var(--color-text);
        font-weight: 500;
        padding: var(--spacing-xs) 0;
        position: relative;
    }
    
    .nav-link::after {
        content: '';
        position: absolute;
        bottom: 0;
        left: 0;
        width: 0;
        height: 2px;
        background-color: var(--color-secondary);
        transition: var(--transition-medium);
    }
    
    .nav-link:hover::after {
        width: 100%;
    }
    
    .nav-toggle {
        display: none;
        background: none;
        border: none;
        cursor: pointer;
        width: 30px;
        height: 22px;
        position: relative;
        z-index: 101;
    }
    
    .nav-toggle span {
        display: block;
        position: absolute;
        height: 2px;
        width: 100%;
        background: var(--color-text);
        transition: var(--transition-medium);
    }
    
    .nav-toggle span:first-child {
        top: 0;
    }
    
    .nav-toggle span:last-child {
        bottom: 0;
    }
    
    .nav-toggle.active span:first-child {
        transform: rotate(45deg) translate(4px, 10px);
    }
    
    .nav-toggle.active span:last-child {
        transform: rotate(-45deg) translate(4px, -10px);
    }
    
    /* --- HERO SECTION --- */
    .hero {
        height: 100vh;
        min-height: 700px;
        display: flex;
        align-items: center;
        padding-top: 80px;
        position: relative;
        background-color: var(--color-background);
    }
    
    .hero-container {
        display: flex;
        align-items: center;
        justify-content: space-between;
        gap: var(--spacing-lg);
        max-width: 1200px;
        margin: 0 auto;
        padding: 0 var(--spacing-md);
        width: 100%;
    }
    
    .hero-content {
        flex: 1;
        max-width: 600px;
    }
    
    .hero-content h1 {
        margin-bottom: var(--spacing-sm);
    }
    
    .hero-buttons {
        display: flex;
        gap: var(--spacing-sm);
        margin-top: var(--spacing-md);
    }
    
    .hero-image {
        flex: 1;
        display: flex;
        justify-content: center;
        align-items: center;
        position: relative;
    }
    
    .image-frame {
        position: relative;
        border-radius: var(--border-radius-lg);
        overflow: hidden;
        max-width: 400px;
        width: 100%;
        aspect-ratio: 4/5;
        box-shadow: var(--shadow-large);
        z-index: 2;
        border: 2px solid var(--color-secondary);
        transition: var(--transition-medium);
    }
    
    .image-frame:hover {
        transform: translate(-5px, -5px);
        box-shadow: 8px 8px 0px var(--color-secondary-transparent);
    }
    
    .placeholder-image {
        width: 100%;
        height: 100%;
        background-color: var(--color-surface);
        display: flex;
        justify-content: center;
        align-items: center;
        font-size: 3rem;
        color: var(--color-text-secondary);
    }
    
    .pattern-dot {
        position: absolute;
        width: 100%;
        height: 100%;
        top: 40px;
        left: 40px;
        
        background-image: radial-gradient(var(--color-border) 1px, transparent 1px);
        background-size: 15px 15px;
        opacity: 0.3;
    }
    
    /* --- BUTTONS --- */
    .button {
        display: inline-flex;
        align-items: center;
        justify-content: center;
        padding: 0.75rem 2rem;
        border-radius: var(--border-radius-md);
        font-weight: 600;
        cursor: pointer;
        transition: var(--transition-fast);
        text-decoration: none;
        border: none;
        outline: none;
        font-family: var(--font-sans);
        font-size: 1rem;
        gap: 8px;
    }
    
    .button.primary {
        background-color: var(--color-secondary);
        color: #ffffff;
    }
    
    .button.primary:hover {
        background-color: var(--color-accent);
        color: #ffffff;
        transform: translateY(-2px);
        box-shadow: 0 4px 12px rgba(94, 138, 241, 0.3);
    }
    
    .button.secondary {
        background-color: transparent;
        border: 1px solid var(--color-secondary);
        color: var(--color-secondary);
    }
    
    .button.secondary:hover {
        background-color: var(--color-secondary-transparent);
        transform: translateY(-2px);
    }
    
    .button.full-width {
        width: 100%;
    }
    
    /* --- SECTION STYLING --- */
    .section-header {
        text-align: center;
        max-width: 800px;
        margin: 0 auto var(--spacing-lg);
        opacity: 0;
        transform: translateY(30px);
        transition: opacity 0.8s ease, transform 0.8s ease;
    }
    
    .section-header.animate {
        opacity: 1;
        transform: translateY(0);
    }
    
    .section-intro {
        font-size: 1.2rem;
        color: var(--color-text-secondary);
        margin-top: var(--spacing-xs);
    }
    
    /* --- ABOUT SECTION --- */
    .about-content {
        display: flex;
        flex-wrap: wrap;
        gap: var(--spacing-lg);
        align-items: flex-start;
    }
    
    .about-text {
        flex: 1;
        min-width: 300px;
    }
    
    .skill-container {
        display: flex;
        flex-wrap: wrap;
        gap: var(--spacing-lg);
        flex: 1;
        min-width: 300px;
    }
    
    .skill-column {
        flex: 1;
        min-width: 250px;
    }
    
    .skill-column h3 { margin-bottom: var(--spacing-sm);
        font-size: 1.3rem;
        color: var(--color-text-tertiary);
    }
    
    .skill-list {
        display: flex;
        flex-direction: column;
        gap: var(--spacing-xs);
    }
    
    .skill-list li {
        position: relative;
        padding-left: 20px;
    }
    
    .skill-list li::before {
        content: "▹";
        position: absolute;
        left: 0;
        color: var(--color-secondary);
    }
    
    /* --- RESEARCH SECTION --- */
    .research-areas {
        display: flex;
        flex-wrap: wrap;
        gap: var(--spacing-md);
        justify-content: center;
    }
    
    .research-card {
        background-color: var(--color-surface);
        border-radius: var(--border-radius-md);
        padding: var(--spacing-md);
        flex: 1;
        min-width: 300px;
        display: flex;
        flex-direction: column;
        box-shadow: var(--shadow-medium);
        border: 1px solid var(--color-border);
        transition: var(--transition-medium);
        opacity: 0;
        transform: translateY(30px);
    }
    
    .research-card.animate {
        opacity: 1;
        transform: translateY(0);
    }
    
    .research-card:hover {
        transform: translateY(-10px);
        box-shadow: var(--shadow-large);
    }
    
    .research-icon {
        font-size: 2.5rem;
        color: var(--color-secondary);
        margin-bottom: var(--spacing-sm);
        text-align: center;
    }
    
    .research-content h3 {
        margin-bottom: var(--spacing-xs);
        text-align: center;
    }
    
    /* --- PUBLICATIONS SECTION --- */
    .publications-list {
        display: flex;
        flex-direction: column;
        gap: var(--spacing-md);
        margin-bottom: var(--spacing-lg);
    }
    
    .pub-item {
        display: flex;
        background-color: var(--color-surface);
        border-radius: var(--border-radius-md);
        overflow: hidden;
        box-shadow: var(--shadow-medium);
        transition: var(--transition-medium);
        border: 1px solid var(--color-border);
        opacity: 0;
        transform: translateX(-30px);
    }
    
    .pub-item.animate {
        opacity: 1;
        transform: translateX(0);
    }
    
    .pub-item:hover {
        transform: translateX(5px);
        box-shadow: var(--shadow-large);
    }
    
    .pub-meta {
        background-color: var(--color-background-alt);
        padding: var(--spacing-md);
        display: flex;
        flex-direction: column;
        align-items: center;
        justify-content: center;
        min-width: 120px;
        border-right: 1px solid var(--color-border);
    }
    
    .pub-year {
        font-size: 1.5rem;
        font-weight: 700;
        color: var(--color-secondary);
        margin-bottom: var(--spacing-xs);
    }
    
    .pub-type {
        font-size: 0.875rem;
        text-transform: uppercase;
        letter-spacing: 1px;
        color: var(--color-text-tertiary);
    }
    
    .pub-details {
        padding: var(--spacing-md);
        flex: 1;
    }
    
    .pub-authors {
        color: var(--color-text-tertiary);
        margin-bottom: var(--spacing-xs);
    }
    
    .pub-venue {
        color: var(--color-text-secondary);
        margin-bottom: var(--spacing-sm);
        font-size: 0.9rem;
    }
    
    .pub-abstract {
        font-size: 0.95rem;
        margin-bottom: var(--spacing-sm);
    }
    
    .pub-links, .project-links {
        display: flex;
        gap: var(--spacing-sm);
        flex-wrap: wrap;
    }
    
    .link-button {
        display: inline-flex;
        align-items: center;
        gap: 8px;
        padding: 6px 12px;
        font-size: 0.875rem;
        border-radius: var(--border-radius-sm);
        background-color: var(--color-secondary-transparent);
        color: var(--color-secondary);
        transition: var(--transition-fast);
    }
    
    .link-button:hover {
        background-color: rgba(94, 138, 241, 0.2);
        color: var(--color-text);
    }
    
    .view-all-container {
        display: flex;
        justify-content: center;
        margin-top: var(--spacing-md);
        opacity: 0;
        transform: translateY(20px);
        transition: opacity 0.8s ease, transform 0.8s ease;
    }
    
    .view-all-container.animate {
        opacity: 1;
        transform: translateY(0);
    }
    
    /* --- PROJECTS SECTION --- */
    .projects-grid {
        display: grid;
        grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
        gap: var(--spacing-md);
    }
    
    .project-card {
        background-color: var(--color-surface);
        border-radius: var(--border-radius-md);
        overflow: hidden;
        box-shadow: var(--shadow-medium);
        transition: var(--transition-medium);
        border: 1px solid var(--color-border);
        height: 100%;
        display: flex;
        flex-direction: column;
        opacity: 0;
        transform: translateY(30px);
    }
    
    .project-card.animate {
        opacity: 1;
        transform: translateY(0);
    }
    
    .project-card:hover {
        transform: translateY(-10px);
        box-shadow: var(--shadow-large);
    }
    
    .project-img {
        height: 200px;
        overflow: hidden;
        border-bottom: 1px solid var(--color-border);
    }
    
    .project-placeholder {
        width: 100%;
        height: 100%;
        background-color: var(--color-background-light);
        display: flex;
        justify-content: center;
        align-items: center;
        font-size: 2rem;
        color: var(--color-text-secondary);
    }
    
    .project-content {
        padding: var(--spacing-md);
        display: flex;
        flex-direction: column;
        flex: 1;
    }
    
    .project-content h3 {
        margin-bottom: var(--spacing-xs);
    }
    
    .project-content p {
        margin-bottom: var(--spacing-md);
        font-size: 0.95rem;
        color: var(--color-text-secondary);
        flex: 1;
    }
    
    .tech-stack {
        display: flex;
        flex-wrap: wrap;
        gap: 8px;
        margin-bottom: var(--spacing-sm);
    }
    
    .tech-stack span {
        background-color: var(--color-primary-light);
        padding: 4px 10px;
        border-radius: var(--border-radius-full);
        font-size: 0.8rem;
        color: var(--color-text-tertiary);
        border: 1px solid var(--color-border);
    }
    
    /* --- CONTACT SECTION --- */
    .contact-container {
        display: flex;
        gap: var(--spacing-lg);
        flex-wrap: wrap;
    }
    
    .contact-container > * {
        opacity: 0;
        transform: translateY(30px);
        transition: opacity 0.8s ease, transform 0.8s ease;
    }
    
    .contact-container > *.animate {
        opacity: 1;
        transform: translateY(0);
    }
    
    .contact-details {
        flex: 1;
        min-width: 300px;
    }
    
    .contact-info {
        margin-bottom: var(--spacing-md);
    }
    
    .contact-item {
        display: flex;
        align-items: flex-start;
        gap: var(--spacing-sm);
        margin-bottom: var(--spacing-sm);
    }
    
    .contact-item i {
        color: var(--color-secondary);
        font-size: 1.5rem;
        margin-top: 5px;
    }
    
    .social-links {
        display: flex;
        gap: var(--spacing-sm);
        margin-top: var(--spacing-md);
    }
    
    .social-icon {
        display: flex;
        justify-content: center;
        align-items: center;
        width: 45px;
        height: 45px;
        border-radius: var(--border-radius-full);
        background-color: var(--color-background-light);
        color: var(--color-text-tertiary);
        font-size: 1.2rem;
        transition: var(--transition-medium);
        border: 1px solid var(--color-border);
    }
    
    .social-icon:hover {
        background-color: var(--color-secondary-transparent); /* soft, subtle */
        color: var(--color-secondary); /* icon turns your accent blue */
        transform: translateY(-5px);
        border-color: var(--color-secondary);
    }
    
    .contact-form {
        flex: 1;
        min-width: 300px;
        background-color: var(--color-surface);
        padding: var(--spacing-md);
        border-radius: var(--border-radius-md);
        box-shadow: var(--shadow-medium);
        border: 1px solid var(--color-border);
    }
    
    .form-row {
        display: flex;
        gap: var(--spacing-sm);
        margin-bottom: var(--spacing-sm);
    }
    
    .form-group {
        margin-bottom: var(--spacing-sm);
        flex: 1;
    }
    
    .form-group label {
        display: block;
        margin-bottom: 8px;
        font-weight: 500;
        color: var(--color-text-tertiary);
    }
    
    .form-group input,
    .form-group textarea {
        width: 100%;
        padding: 12px 15px;
        background-color: var(--color-background-light);
        border: 1px solid var(--color-border);
        border-radius: var(--border-radius-sm);
        color: var(--color-text);
        font-family: var(--font-sans);
        font-size: 1rem;
        transition: var(--transition-fast);
    }
    
    .form-group input:focus,
    .form-group textarea:focus {
        outline: none;
        border-color: var(--color-secondary);
        box-shadow: 0 0 0 3px rgba(94, 138, 241, 0.2);
    }
    
    /* --- FOOTER --- */
    footer {
        background-color: var(--color-background-light);
        padding: var(--spacing-md) 0;
        border-top: 1px solid var(--color-border);
        margin-top: var(--spacing-md);
    }
    
    .footer-content {
        display: flex;
        justify-content: space-between;
        align-items: center;
        flex-wrap: wrap;
        gap: var(--spacing-md);
    }
    
    .footer-left {
        display: flex;
        align-items: center;
        gap: var(--spacing-sm);
    }
    
    .footer-logo {
        font-family: var(--font-serif);
        font-size: 1.5rem;
        font-weight: 700;
        color: var(--color-secondary);
    }
    
    .footer-left p {
        margin-bottom: 0;
        color: var(--color-text-secondary);
    }
    
    .footer-right {
        text-align: right;
    }
    
    .footer-nav {
        display: flex;
        gap: var(--spacing-md);
        margin-bottom: var(--spacing-xs);
    }
    
    .footer-nav a {
        color: var(--color-text-secondary);
        font-size: 0.9rem;
        transition: var(--transition-fast);
    }
    
    .footer-nav a:hover {
        color: var(--color-secondary);
    }
    
    .copyright {
        font-size: 0.875rem;
        color: var(--color-text-secondary);
        margin-bottom: 0;
    }
    
    /* --- ANIMATIONS --- */
    @keyframes fadeIn {
        from { opacity: 0; transform: translateY(20px); }
        to { opacity: 1; transform: translateY(0); }
    }
    
    /* --- RESPONSIVE STYLES --- */
    @media (max-width: 992px) {
        h1 {
            font-size: 3rem;
        }
        
        h2 {
            font-size: 2rem;
        }
        
        .hero {
            height: auto;
            padding: 150px 0 100px;
        }
        
        .hero-container {
            flex-direction: column;
            text-align: center;
        }
        
        .hero-buttons {
            justify-content: center;
        }
        
        .hero-image {
            margin-top: var(--spacing-lg);
        }
        
        .image-frame {
            max-width: 300px;
        }
        
        .about-content,
        .contact-container {
            flex-direction: column;
        }
    }
    
    @media (max-width: 768px) {
        .section {
            padding: var(--spacing-lg) 0;
        }
        
        .nav-menu {
            padding-top:30px;
            padding-bottom: 30px;
            position: fixed;
            top: 0;
            right: 0;
            bottom: 10;
            background-color: var(--color-background-alt);
            width: 75%;
            max-width: 300px;
            flex-direction: column;
            justify-content: center;
            align-items: center;
            transform: translateX(100%);
            transition: transform var(--transition-medium);
            box-shadow: var(--shadow-large);
            z-index: 100;
        }
        
        .nav-menu.active {
            transform: translateX(0);
        }
        
        .nav-toggle {
            display: block;
        }
        
        .footer-content {
            flex-direction: column;
            text-align: center;
        }
        
        .footer-right {
            text-align: center;
        }
        
        .footer-nav {
            justify-content: center;
        }
        
        .form-row {
            flex-direction: column;
        }
    }
    
    @media (max-width: 576px) {
        h1 {
            font-size: 2.5rem;
        }
        
        h2 {
            font-size: 1.8rem;
        }
        
        .pub-item {
            flex-direction: column;
        }
        
        .pub-meta {
            flex-direction: row;
            justify-content: space-between;
            border-right: none;
            border-bottom: 1px solid var(--color-border);
        }
        
        .projects-grid {
            grid-template-columns: 1fr;
        }
        
        .hero {
            padding: 120px 0 80px;
        }
    }

    .invalid-feedback {
        color: #d9534f;
        font-size: 0.85rem;
        margin-top: 4px;
        display: none;
    }

    .was-validated input:invalid ~ .invalid-feedback,
    .was-validated textarea:invalid ~ .invalid-feedback {
        display: block;
    }

    .was-validated input:invalid,
    .was-validated textarea:invalid {
        border-color: #d9534f;
    }

    .was-validated input:valid,
    .was-validated textarea:valid {
        border-color: #28a745;
    }
    .spinner {
        border: 3px solid rgba(255, 255, 255, 0.3); /* faint white base */
        border-top: 3px solid #ffffff;
        border-radius: 50%;
        width: 1rem;
        height: 1rem;
        animation: spin 1s linear infinite;
    }

    @keyframes spin {
        100% { transform: rotate(360deg); }
    }