/* ============================================
   CSS Variables - Color Scheme, Typography, Spacing
   ============================================ */
:root {
    /* Color Scheme */
    --color-primary: #667eea;
    --color-primary-dark: #5568d3;
    --color-secondary: #764ba2;
    --color-accent: #ff9800;
    --color-accent-light: #ffb74d;

    /* Text Colors */
    --color-text-primary: #2c3e50;
    --color-text-secondary: #555555;
    --color-text-light: #666666;
    --color-text-white: #ffffff;

    /* Background Colors */
    --color-bg-white: #ffffff;
    --color-bg-light: #f8f9fa;
    --color-bg-lighter: #f0f2f5;
    --color-bg-accent: #fff3e0;

    /* Border Colors */
    --color-border: #e0e0e0;
    --color-border-light: #eeeeee;

    /* Typography */
    --font-family-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-family-heading: 'Roboto', 'Open Sans', sans-serif;

    --font-size-base: 1rem;
    --font-size-sm: 0.875rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;

    --font-weight-normal: 400;
    --font-weight-medium: 500;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;

    --line-height-base: 1.6;
    --line-height-heading: 1.2;

    /* Spacing Scale (8px base) */
    --spacing-xs: 0.5rem;
    /* 8px */
    --spacing-sm: 1rem;
    /* 16px */
    --spacing-md: 1.5rem;
    /* 24px */
    --spacing-lg: 2rem;
    /* 32px */
    --spacing-xl: 3rem;
    /* 48px */
    --spacing-2xl: 4rem;
    /* 64px */
    --spacing-3xl: 5rem;
    /* 80px */

    /* Layout */
    --container-max-width: 1200px;
    --container-padding: 1.25rem;
    /* 20px */

    /* Border Radius */
    --border-radius-sm: 4px;
    --border-radius-md: 8px;
    --border-radius-lg: 12px;

    /* Shadows */
    --shadow-sm: 0 2px 4px rgba(0, 0, 0, 0.08);
    --shadow-md: 0 2px 8px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 4px 16px rgba(0, 0, 0, 0.12);

    /* Transitions */
    --transition-fast: 0.2s ease;
    --transition-base: 0.3s ease;
}

/* ============================================
   Base Styles - Mobile First
   ============================================ */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family-base);
    font-size: var(--font-size-base);
    line-height: var(--line-height-base);
    color: var(--color-text-secondary);
    background-color: var(--color-bg-white);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* Container */
.container {
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--container-padding);
    width: 100%;
}

/* ============================================
   Navigation Bar Styles
   ============================================ */
header {
    background-color: var(--color-bg-white);
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 1000;
    transition: box-shadow var(--transition-base);
}

#main-nav {
    padding: var(--spacing-sm) 0;
}

.nav-container {
    max-width: var(--container-max-width);
    margin: 0 auto;
    padding: 0 var(--container-padding);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-sm);
}

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

.nav-logo {
    height: 40px;
    width: auto;
    border-radius: var(--border-radius-sm);
}

.nav-brand h1 {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-primary);
    text-align: center;
    margin: 0;
}

.nav-menu {
    list-style: none;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: var(--spacing-xs);
    padding: 0;
    margin: 0;
}

.nav-menu li {
    margin: 0;
}

.nav-menu a {
    display: block;
    padding: var(--spacing-xs) var(--spacing-sm);
    color: var(--color-text-primary);
    text-decoration: none;
    font-weight: var(--font-weight-medium);
    font-size: 0.9rem;
    border-radius: var(--border-radius-sm);
    transition: all var(--transition-fast);
    position: relative;
}

.nav-menu a:hover {
    color: var(--color-primary);
    background-color: var(--color-bg-light);
}

.nav-menu a.active {
    color: var(--color-primary);
    background-color: var(--color-bg-light);
    font-weight: var(--font-weight-semibold);
}

.nav-menu a.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: var(--spacing-sm);
    right: var(--spacing-sm);
    height: 2px;
    background-color: var(--color-primary);
}

/* Mobile Menu Toggle Button */
.menu-toggle {
    display: none;
    flex-direction: column;
    justify-content: space-around;
    width: 2rem;
    height: 2rem;
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 0;
    z-index: 10;
}

.menu-toggle span {
    width: 2rem;
    height: 0.25rem;
    background-color: var(--color-text-primary);
    border-radius: 10px;
    transition: all var(--transition-base);
    position: relative;
    transform-origin: 1px;
}

.menu-toggle.active span:nth-child(1) {
    transform: rotate(45deg);
}

.menu-toggle.active span:nth-child(2) {
    opacity: 0;
    transform: translateX(20px);
}

.menu-toggle.active span:nth-child(3) {
    transform: rotate(-45deg);
}

/* Mobile Menu Styles */
@media (max-width: 767px) {
    .menu-toggle {
        display: flex;
        position: absolute;
        right: var(--container-padding);
        top: 50%;
        transform: translateY(-50%);
    }

    .nav-container {
        position: relative;
    }

    .nav-menu {
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background-color: var(--color-bg-white);
        flex-direction: column;
        align-items: stretch;
        padding: var(--spacing-sm) var(--container-padding);
        box-shadow: var(--shadow-md);
        max-height: 0;
        overflow: hidden;
        opacity: 0;
        transition: all var(--transition-base);
        margin-top: var(--spacing-sm);
    }

    .nav-menu.active {
        max-height: 500px;
        opacity: 1;
    }

    .nav-menu li {
        width: 100%;
    }

    .nav-menu a {
        width: 100%;
        text-align: left;
        padding: var(--spacing-sm) var(--spacing-md);
    }

    .nav-menu a.active::after {
        left: 0;
        right: auto;
        width: 4px;
        height: 100%;
        bottom: auto;
        top: 0;
    }
}

/* ============================================
   Hero Section Styles
   ============================================ */
.hero-section {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-secondary) 100%);
    color: var(--color-text-white);
    padding: var(--spacing-3xl) var(--container-padding);
    text-align: center;
}

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

.hero-title {
    font-size: 1.75rem;
    font-weight: var(--font-weight-bold);
    line-height: var(--line-height-heading);
    margin-bottom: var(--spacing-md);
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

.hero-subtitle {
    font-size: 1.1rem;
    font-weight: var(--font-weight-normal);
    line-height: var(--line-height-base);
    opacity: 0.95;
    max-width: 700px;
    margin: 0 auto;
}

/* Hero Registration Button */
.button-container {
    margin-top: var(--spacing-lg);
}

.register-button {
    display: inline-block;
    background-color: var(--color-text-white);
    color: var(--color-primary);
    padding: var(--spacing-sm) var(--spacing-xl);
    border-radius: var(--border-radius-md);
    text-decoration: none;
    font-weight: var(--font-weight-bold);
    font-size: var(--font-size-lg);
    transition: all var(--transition-base);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.2);
}

.register-button:hover {
    background-color: #f0f0f0;
    transform: translateY(-2px);
    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.3);
}

.register-button.large {
    padding: var(--spacing-md) var(--spacing-2xl);
    font-size: var(--font-size-xl);
}

/* ============================================
   Section Base Styles
   ============================================ */
.section {
    padding: var(--spacing-2xl) var(--container-padding);
}

.section h2 {
    font-size: 1.75rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-lg);
    text-align: center;
    line-height: var(--line-height-heading);
}

.section h3 {
    font-size: 1.3rem;
    font-weight: var(--font-weight-semibold);
    color: var(--color-text-primary);
    margin-top: var(--spacing-lg);
    margin-bottom: var(--spacing-sm);
    line-height: var(--line-height-heading);
}

.section h4 {
    font-size: 1.1rem;
    font-weight: var(--font-weight-semibold);
    color: var(--color-text-primary);
    margin-top: var(--spacing-md);
    margin-bottom: var(--spacing-sm);
}

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

.section ul,
.section ol {
    margin-bottom: var(--spacing-md);
    padding-left: var(--spacing-lg);
}

.section li {
    font-size: 1rem;
    line-height: 1.7;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xs);
}

/* ============================================
   Overview Section Styles
   ============================================ */
.overview-section {
    background-color: var(--color-bg-light);
}

.overview-content {
    max-width: 800px;
    margin: 0 auto;
}

.objectives-list {
    list-style-type: none;
    padding-left: 0;
    margin: var(--spacing-md) 0;
}

.objectives-list li {
    font-size: 1rem;
    line-height: 1.7;
    color: var(--color-text-secondary);
    padding: var(--spacing-sm) 0 var(--spacing-sm) var(--spacing-lg);
    position: relative;
}

.objectives-list li:before {
    content: "✓";
    position: absolute;
    left: 0;
    color: var(--color-primary);
    font-weight: var(--font-weight-bold);
    font-size: 1.2rem;
}

/* ============================================
   Important Dates Section Styles
   ============================================ */
.dates-section {
    background-color: var(--color-bg-white);
}

.dates-content {
    max-width: 700px;
    margin: 0 auto;
}

.dates-intro {
    text-align: center;
    font-size: var(--font-size-sm);
    color: var(--color-text-light);
    margin-bottom: var(--spacing-lg);
    font-style: italic;
}

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

.date-item {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
    padding: var(--spacing-sm) var(--spacing-md);
    background-color: var(--color-bg-light);
    border-radius: var(--border-radius-md);
    border-left: 4px solid var(--color-border);
    transition: all var(--transition-base);
}

.date-item:hover {
    background-color: var(--color-bg-lighter);
    transform: translateX(4px);
}

.date-item.upcoming {
    background-color: var(--color-bg-accent);
    border-left-color: var(--color-accent);
    box-shadow: 0 2px 8px rgba(255, 152, 0, 0.15);
}

.date-item.upcoming:hover {
    background-color: #ffe8cc;
    box-shadow: 0 4px 12px rgba(255, 152, 0, 0.2);
}

.date-event {
    font-size: 1rem;
    font-weight: var(--font-weight-medium);
    color: var(--color-text-primary);
}

.date-item.upcoming .date-event {
    color: #e65100;
    font-weight: var(--font-weight-semibold);
}

.date-value {
    font-size: 1rem;
    font-weight: var(--font-weight-semibold);
    color: var(--color-primary);
    padding: var(--spacing-xs) var(--spacing-sm);
    background-color: var(--color-bg-white);
    border-radius: var(--border-radius-sm);
    text-align: center;
    align-self: flex-start;
}

.date-item.upcoming .date-value {
    color: var(--color-accent);
    background-color: var(--color-bg-white);
    border: 2px solid var(--color-accent);
}

/* ============================================
   Task Description Section Styles
   ============================================ */
.task-section {
    background-color: var(--color-bg-light);
}

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

.dataset-list,
.metrics-list {
    list-style-type: disc;
    padding-left: var(--spacing-lg);
}

.code-block {
    background-color: var(--color-text-primary);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-md);
    margin: var(--spacing-md) 0;
    overflow-x: auto;
}

.code-block pre {
    margin: 0;
}

.code-block code {
    font-family: 'Courier New', Courier, monospace;
    font-size: 0.9rem;
    color: #a8dadc;
    line-height: 1.5;
}

/* ============================================
   Submission Section Styles
   ============================================ */
.submission-section {
    background-color: var(--color-bg-white);
}

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

.submission-steps {
    counter-reset: step-counter;
    list-style: none;
    padding-left: 0;
}

.submission-steps li {
    counter-increment: step-counter;
    position: relative;
    padding-left: var(--spacing-xl);
    margin-bottom: var(--spacing-md);
}

.submission-steps li::before {
    content: counter(step-counter);
    position: absolute;
    left: 0;
    top: 0;
    width: 2rem;
    height: 2rem;
    background-color: var(--color-primary);
    color: var(--color-text-white);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: var(--font-weight-bold);
    font-size: 1rem;
}

.submission-steps li strong {
    color: var(--color-text-primary);
    font-weight: var(--font-weight-semibold);
}

.submission-rules {
    list-style-type: none;
    padding-left: 0;
}

.submission-rules li {
    padding: var(--spacing-sm);
    margin-bottom: var(--spacing-sm);
    background-color: var(--color-bg-light);
    border-left: 4px solid var(--color-primary);
    border-radius: var(--border-radius-sm);
}

/* ============================================
   Organizers Section Styles
   ============================================ */
.organizers-section {
    background-color: var(--color-bg-light);
}

.organizers-content {
    max-width: 1000px;
    margin: 0 auto;
}

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

.organizers-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-xl);
    margin-bottom: var(--spacing-xl);
    max-width: 1000px;
    margin-left: auto;
    margin-right: auto;
}

.organizer-card {
    background-color: var(--color-bg-white);
    border-radius: var(--border-radius-md);
    padding: var(--spacing-xl) var(--spacing-md);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
    border: none;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
}

.organizer-card:hover {
    box-shadow: var(--shadow-lg);
    transform: translateY(-4px);
}

.organizer-photo {
    width: 180px;
    height: 180px;
    border-radius: 50%;
    overflow: hidden;
    margin-bottom: var(--spacing-lg);
    border: 5px solid #2d8659;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.organizer-photo img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    display: block;
}

.organizer-info {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
    width: 100%;
    align-items: center;
}

.organizer-name {
    font-size: 1.5rem;
    font-weight: var(--font-weight-bold);
    color: var(--color-text-primary);
    margin: 0 0 var(--spacing-sm) 0;
    line-height: 1.3;
}

.organizer-affiliation {
    font-size: 1.05rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin: 0 0 var(--spacing-md) 0;
    font-weight: var(--font-weight-normal);
}

.organizer-role {
    font-size: var(--font-size-sm);
    color: var(--color-text-light);
    font-weight: var(--font-weight-normal);
    text-transform: none;
    letter-spacing: 0;
    margin: 0 0 var(--spacing-sm) 0;
    display: none;
}

.organizer-email {
    font-size: var(--font-size-sm);
    color: var(--color-primary);
    text-decoration: none;
    transition: color var(--transition-fast);
    word-break: break-word;
}

.organizer-email:hover {
    color: var(--color-secondary);
    text-decoration: underline;
}

.organizer-link {
    font-size: 1rem;
    color: #5b4fc4;
    text-decoration: underline;
    transition: color var(--transition-fast);
    word-break: break-word;
    font-weight: var(--font-weight-medium);
    margin-top: var(--spacing-xs);
}

.organizer-link:hover {
    color: #4a3fa0;
}

.contact-info {
    text-align: center;
    padding: var(--spacing-md);
    background-color: var(--color-bg-white);
    border-radius: var(--border-radius-md);
    border: 2px solid var(--color-border);
    overflow-wrap: break-word;
    word-wrap: break-word;
    word-break: break-word;
}

.contact-info p {
    font-size: var(--font-size-lg);
    color: var(--color-text-secondary);
    margin: 0;
    overflow-wrap: break-word;
    word-wrap: break-word;
}

.contact-info a {
    color: var(--color-primary);
    text-decoration: none;
    font-weight: var(--font-weight-medium);
    transition: color var(--transition-fast);
    overflow-wrap: break-word;
    word-wrap: break-word;
    word-break: break-all;
    display: inline-block;
    max-width: 100%;
}

.contact-info a:hover {
    color: var(--color-secondary);
    text-decoration: underline;
}

/* Mobile-specific email styling */
@media (max-width: 767px) {
    .contact-info {
        padding: var(--spacing-sm);
    }

    .contact-info p {
        font-size: var(--font-size-sm);
        line-height: 1.6;
    }

    .contact-info a {
        font-size: var(--font-size-sm);
    }
}

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

footer p {
    margin: 0;
    font-size: var(--font-size-sm);
    opacity: 0.9;
}

/* ============================================
   Media Queries - Tablet (768px+)
   ============================================ */
@media (min-width: 768px) {

    /* Navigation */
    .nav-container {
        flex-direction: row;
        justify-content: space-between;
        align-items: center;
    }

    .nav-logo {
        height: 50px;
    }

    .nav-brand h1 {
        font-size: 1.5rem;
    }

    .nav-menu {
        gap: var(--spacing-sm);
    }

    .nav-menu a {
        font-size: 1rem;
        padding: var(--spacing-xs) var(--spacing-md);
    }

    /* Hero Section */
    .hero-section {
        padding: var(--spacing-3xl) var(--container-padding);
    }

    .hero-title {
        font-size: 2.25rem;
    }

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

    /* Section Headings */
    .section h2 {
        font-size: 2rem;
    }

    .section h3 {
        font-size: 1.5rem;
    }

    .section h4 {
        font-size: 1.2rem;
    }

    .section p {
        font-size: var(--font-size-lg);
    }

    .section li {
        font-size: var(--font-size-lg);
    }

    /* Dates Section */
    .date-item {
        flex-direction: row;
        justify-content: space-between;
        align-items: center;
        padding: var(--spacing-md) var(--spacing-lg);
    }

    .date-event {
        font-size: var(--font-size-lg);
    }

    .date-value {
        font-size: var(--font-size-lg);
        min-width: 120px;
    }

    /* Organizers Grid */
    .organizers-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: var(--spacing-xl);
    }

    .organizer-card {
        padding: var(--spacing-xl) var(--spacing-lg);
    }

    .organizer-photo {
        width: 200px;
        height: 200px;
    }

    .organizer-name {
        font-size: 1.6rem;
    }

    .organizer-affiliation {
        font-size: 1.1rem;
    }
}

/* ============================================
   Media Queries - Desktop (1024px+)
   ============================================ */
@media (min-width: 1024px) {

    /* Container */
    .container {
        padding: 0 var(--spacing-lg);
    }

    /* Navigation */
    .nav-logo {
        height: 60px;
    }

    .nav-brand h1 {
        font-size: 1.75rem;
    }

    .nav-menu {
        gap: var(--spacing-md);
    }

    /* Hero Section */
    .hero-title {
        font-size: 2.5rem;
    }

    .hero-subtitle {
        font-size: var(--font-size-xl);
    }

    /* Section Spacing */
    .section {
        padding: var(--spacing-3xl) var(--container-padding);
    }

    /* Organizers Grid - 4 columns on large screens */
    .organizers-grid {
        grid-template-columns: repeat(4, 1fr);
    }

    .organizer-photo {
        width: 180px;
        height: 180px;
    }

    /* Code blocks */
    .code-block {
        padding: var(--spacing-lg);
    }
}

/* ============================================
   Media Queries - Large Desktop (1440px+)
   ============================================ */
@media (min-width: 1440px) {
    .hero-title {
        font-size: 3rem;
    }

    .section h2 {
        font-size: 2.25rem;
    }
}

/* ============================================
   Kaggle Signup Styles
   ============================================ */
.kaggle-signup-box {
    background: linear-gradient(135deg, #20beff 0%, #1a8fd9 100%);
    color: var(--color-text-white);
    padding: var(--spacing-lg);
    border-radius: var(--border-radius-lg);
    margin-bottom: var(--spacing-xl);
    text-align: center;
    box-shadow: var(--shadow-lg);
}

.kaggle-signup-box h3 {
    color: var(--color-text-white);
    margin-top: 0;
    margin-bottom: var(--spacing-sm);
    font-size: 1.5rem;
}

.kaggle-signup-box p {
    color: var(--color-text-white);
    margin-bottom: var(--spacing-sm);
}

.kaggle-button {
    display: inline-block;
    background-color: var(--color-text-white);
    color: #1a8fd9;
    padding: var(--spacing-sm) var(--spacing-xl);
    border-radius: var(--border-radius-md);
    text-decoration: none;
    font-weight: var(--font-weight-bold);
    font-size: var(--font-size-lg);
    transition: all var(--transition-base);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.kaggle-button:hover {
    background-color: #f0f0f0;
    transform: translateY(-2px);
    box-shadow: 0 6px 16px rgba(0, 0, 0, 0.2);
}

.kaggle-link {
    color: var(--color-primary);
    font-weight: var(--font-weight-semibold);
    text-decoration: underline;
    transition: color var(--transition-fast);
}

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