/* =========================================
   STEM Learning Hub - Main Stylesheet
   Minimal, clean design for 8th graders
   ========================================= */

/* CSS Variables */
:root {
    /* Colors */
    --primary-color: #4361ee;
    --primary-dark: #3651d4;
    --secondary-color: #7209b7;
    
    /* Subject Colors */
    --science-color: #10b981;
    --technology-color: #3b82f6;
    --engineering-color: #f59e0b;
    --mathematics-color: #ef4444;
    
    /* Neutral Colors */
    --text-primary: #1f2937;
    --text-secondary: #4b5563;
    --text-light: #9ca3af;
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;
    --border-color: #e5e7eb;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    --spacing-3xl: 4rem;
    
    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 2rem;
    --font-size-4xl: 2.5rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-full: 9999px;
    
    /* Shadows */
    --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);
    
    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 350ms ease;
}

/* Reset & Base Styles */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-primary);
    min-height: 100vh;
}

a {
    text-decoration: none;
    color: inherit;
}

ul, ol {
    list-style: none;
}

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

button {
    font-family: inherit;
    cursor: pointer;
    border: none;
    background: none;
}

input {
    font-family: inherit;
}

/* Container */
.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
}

/* =========================================
   Navigation
   ========================================= */
.navbar {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    padding: var(--spacing-md) 0;
}

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

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-weight: 700;
    font-size: var(--font-size-xl);
    color: var(--primary-color);
}

.logo-icon {
    font-size: 1.5rem;
}

.nav-menu {
    display: flex;
    gap: var(--spacing-xl);
}

.nav-link {
    font-weight: 500;
    color: var(--text-secondary);
    padding: var(--spacing-sm) 0;
    position: relative;
    transition: color var(--transition-fast);
}

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

.nav-link.active::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: var(--primary-color);
    border-radius: var(--radius-full);
}

/* Mobile Navigation Toggle */
.nav-toggle {
    display: none;
    flex-direction: column;
    gap: 5px;
    padding: var(--spacing-sm);
}

.nav-toggle span {
    display: block;
    width: 24px;
    height: 2px;
    background: var(--text-primary);
    transition: var(--transition-fast);
}

/* =========================================
   Hero Section
   ========================================= */
.hero {
    padding: var(--spacing-3xl) 0;
    background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-primary) 100%);
    position: relative;
    overflow: hidden;
}

.hero-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
    text-align: center;
    position: relative;
    z-index: 1;
}

.hero-title {
    font-size: clamp(var(--font-size-2xl), 5vw, var(--font-size-4xl));
    font-weight: 700;
    margin-bottom: var(--spacing-lg);
    color: var(--text-primary);
}

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

.hero-subtitle {
    font-size: var(--font-size-lg);
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto var(--spacing-xl);
}

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

/* Floating Icons Animation */
.hero-illustration {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    pointer-events: none;
}

.floating-icons {
    position: relative;
    width: 100%;
    height: 100%;
}

.float-icon {
    position: absolute;
    font-size: 2rem;
    opacity: 0.3;
    animation: float 6s ease-in-out infinite;
}

.icon-1 { top: 10%; left: 10%; animation-delay: 0s; }
.icon-2 { top: 20%; right: 15%; animation-delay: 1s; }
.icon-3 { bottom: 30%; left: 8%; animation-delay: 2s; }
.icon-4 { bottom: 20%; right: 10%; animation-delay: 3s; }
.icon-5 { top: 40%; left: 20%; animation-delay: 4s; }
.icon-6 { top: 50%; right: 20%; animation-delay: 5s; }

@keyframes float {
    0%, 100% { transform: translateY(0) rotate(0deg); }
    50% { transform: translateY(-20px) rotate(5deg); }
}

/* =========================================
   Buttons
   ========================================= */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-md) var(--spacing-xl);
    font-weight: 600;
    font-size: var(--font-size-base);
    border-radius: var(--radius-lg);
    transition: all var(--transition-fast);
}

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

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

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

.btn-secondary:hover {
    background: var(--border-color);
}

.btn-small {
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: var(--font-size-sm);
}

/* =========================================
   Section Styles
   ========================================= */
section {
    padding: var(--spacing-3xl) 0;
}

.section-title {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    text-align: center;
    margin-bottom: var(--spacing-md);
}

.section-description {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-2xl);
}

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

.about-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-xl);
}

.about-card {
    background: var(--bg-primary);
    padding: var(--spacing-xl);
    border-radius: var(--radius-xl);
    text-align: center;
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-base);
}

.about-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.about-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.about-card h3 {
    font-size: var(--font-size-xl);
    margin-bottom: var(--spacing-sm);
}

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

/* =========================================
   Subjects Section
   ========================================= */
.subjects-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-xl);
}

.subject-card {
    background: var(--bg-primary);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    transition: all var(--transition-base);
    display: block;
}

.subject-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.subject-card.science { border-color: var(--science-color); }
.subject-card.technology { border-color: var(--technology-color); }
.subject-card.engineering { border-color: var(--engineering-color); }
.subject-card.mathematics { border-color: var(--mathematics-color); }

.subject-card.science:hover { background: rgba(16, 185, 129, 0.05); }
.subject-card.technology:hover { background: rgba(59, 130, 246, 0.05); }
.subject-card.engineering:hover { background: rgba(245, 158, 11, 0.05); }
.subject-card.mathematics:hover { background: rgba(239, 68, 68, 0.05); }

.subject-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.subject-card h3 {
    font-size: var(--font-size-xl);
    margin-bottom: var(--spacing-sm);
}

.subject-card > p {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

.subject-topics {
    margin-bottom: var(--spacing-lg);
}

.subject-topics li {
    padding: var(--spacing-xs) 0;
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
}

.subject-topics li::before {
    content: '✓ ';
    color: var(--science-color);
}

.subject-card.technology .subject-topics li::before { color: var(--technology-color); }
.subject-card.engineering .subject-topics li::before { color: var(--engineering-color); }
.subject-card.mathematics .subject-topics li::before { color: var(--mathematics-color); }

.subject-link {
    font-weight: 600;
    color: var(--primary-color);
}

/* =========================================
   Facts Carousel
   ========================================= */
.facts-section {
    background: var(--bg-secondary);
}

.facts-carousel {
    position: relative;
    max-width: 600px;
    margin: 0 auto;
    min-height: 150px;
}

.fact-card {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    background: var(--bg-primary);
    padding: var(--spacing-xl);
    border-radius: var(--radius-xl);
    text-align: center;
    box-shadow: var(--shadow-md);
    opacity: 0;
    transform: translateX(50px);
    transition: all var(--transition-base);
}

.fact-card.active {
    opacity: 1;
    transform: translateX(0);
}

.fact-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.fact-text {
    font-size: var(--font-size-lg);
    color: var(--text-primary);
}

.fact-dots {
    display: flex;
    justify-content: center;
    gap: var(--spacing-sm);
    margin-top: var(--spacing-xl);
}

.dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    background: var(--border-color);
    transition: var(--transition-fast);
}

.dot.active {
    background: var(--primary-color);
}

/* =========================================
   Page Headers
   ========================================= */
.page-header {
    padding: var(--spacing-3xl) 0;
    text-align: center;
}

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

.page-icon {
    font-size: 4rem;
    display: block;
    margin-bottom: var(--spacing-md);
}

.page-header h1 {
    font-size: var(--font-size-4xl);
    font-weight: 700;
    margin-bottom: var(--spacing-md);
}

.page-header p {
    font-size: var(--font-size-lg);
    color: var(--text-secondary);
}

/* Subject-specific header colors */
.science-header { background: linear-gradient(135deg, rgba(16, 185, 129, 0.1) 0%, var(--bg-primary) 100%); }
.technology-header { background: linear-gradient(135deg, rgba(59, 130, 246, 0.1) 0%, var(--bg-primary) 100%); }
.engineering-header { background: linear-gradient(135deg, rgba(245, 158, 11, 0.1) 0%, var(--bg-primary) 100%); }
.mathematics-header { background: linear-gradient(135deg, rgba(239, 68, 68, 0.1) 0%, var(--bg-primary) 100%); }

/* =========================================
   Main Content Area
   ========================================= */
.main-content {
    padding: var(--spacing-2xl) 0;
}

/* Topic Navigation */
.topic-nav {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-2xl);
    flex-wrap: wrap;
    justify-content: center;
}

.topic-btn {
    padding: var(--spacing-md) var(--spacing-xl);
    background: var(--bg-tertiary);
    border-radius: var(--radius-lg);
    font-weight: 500;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.topic-btn:hover {
    background: var(--border-color);
}

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

/* Topic Sections */
.topic-section {
    display: none;
}

.topic-section.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.topic-title {
    font-size: var(--font-size-2xl);
    margin-bottom: var(--spacing-xl);
    color: var(--text-primary);
}

/* =========================================
   Lesson Cards
   ========================================= */
.lesson-card {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    margin-bottom: var(--spacing-xl);
}

.lesson-card h3 {
    font-size: var(--font-size-xl);
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.lesson-card p {
    color: var(--text-secondary);
    margin-bottom: var(--spacing-md);
}

.concept-list {
    margin-left: var(--spacing-xl);
    margin-bottom: var(--spacing-md);
}

.concept-list li {
    position: relative;
    padding: var(--spacing-xs) 0;
    color: var(--text-secondary);
}

.concept-list li::before {
    content: '•';
    position: absolute;
    left: -1rem;
    color: var(--primary-color);
}

/* Example Box */
.example-box {
    background: var(--bg-secondary);
    border-left: 4px solid var(--primary-color);
    padding: var(--spacing-lg);
    border-radius: 0 var(--radius-md) var(--radius-md) 0;
    margin: var(--spacing-md) 0;
}

.example-box h4 {
    font-size: var(--font-size-base);
    margin-bottom: var(--spacing-sm);
    color: var(--text-primary);
}

.example-box p {
    margin: 0;
    color: var(--text-secondary);
}

.example-box.small {
    padding: var(--spacing-md);
}

/* Formula Box */
.formula-box {
    background: var(--bg-tertiary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    margin: var(--spacing-md) 0;
}

.formula {
    font-family: 'Courier New', monospace;
    font-size: var(--font-size-xl);
    font-weight: 600;
    color: var(--primary-color);
}

.formula-box.large .formula {
    font-size: var(--font-size-2xl);
}

/* =========================================
   Law Cards (Newton's Laws)
   ========================================= */
.law-card {
    background: var(--bg-secondary);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    margin: var(--spacing-md) 0;
}

.law-number {
    display: inline-block;
    background: var(--primary-color);
    color: white;
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--radius-full);
    font-weight: 600;
    font-size: var(--font-size-sm);
    margin-bottom: var(--spacing-sm);
}

.law-card h4 {
    font-size: var(--font-size-lg);
    margin-bottom: var(--spacing-sm);
}

/* =========================================
   Quiz Card
   ========================================= */
.quiz-card {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--secondary-color) 100%);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    color: white;
}

.quiz-card h3 {
    color: white;
    margin-bottom: var(--spacing-lg);
}

.quiz-question p {
    color: rgba(255, 255, 255, 0.9);
}

.quiz-options {
    display: grid;
    gap: var(--spacing-sm);
    margin: var(--spacing-lg) 0;
}

.quiz-option {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    background: rgba(255, 255, 255, 0.15);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition-fast);
}

.quiz-option:hover {
    background: rgba(255, 255, 255, 0.25);
}

.quiz-option input {
    accent-color: white;
}

.quiz-option span {
    color: white;
}

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

.check-answer:hover {
    background: var(--bg-secondary);
}

.quiz-feedback {
    margin-top: var(--spacing-md);
    font-weight: 500;
}

.quiz-feedback.correct {
    color: #4ade80;
}

.quiz-feedback.incorrect {
    color: #fbbf24;
}

/* =========================================
   States of Matter Grid
   ========================================= */
.states-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.state-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
}

.state-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
}

.state-card h4 {
    margin-bottom: var(--spacing-sm);
}

.state-example {
    font-size: var(--font-size-sm);
    color: var(--text-light);
    margin-top: var(--spacing-sm);
}

/* =========================================
   Elements Showcase
   ========================================= */
.elements-showcase {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-md);
    justify-content: center;
    margin-top: var(--spacing-lg);
}

.element-card {
    width: 100px;
    height: 120px;
    background: var(--element-color, var(--primary-color));
    border-radius: var(--radius-lg);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    color: white;
    text-align: center;
    transition: transform var(--transition-fast);
}

.element-card:hover {
    transform: scale(1.1);
}

.element-number {
    font-size: var(--font-size-sm);
    opacity: 0.8;
}

.element-symbol {
    font-size: var(--font-size-2xl);
    font-weight: 700;
}

.element-name {
    font-size: var(--font-size-sm);
    opacity: 0.9;
}

/* =========================================
   Chemical Reaction
   ========================================= */
.reaction-example {
    background: var(--bg-secondary);
    padding: var(--spacing-xl);
    border-radius: var(--radius-lg);
    margin-top: var(--spacing-lg);
}

.reaction-equation {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    font-family: 'Courier New', monospace;
    font-size: var(--font-size-xl);
    margin: var(--spacing-md) 0;
    flex-wrap: wrap;
}

.arrow {
    font-size: var(--font-size-2xl);
    color: var(--primary-color);
}

.reaction-words {
    text-align: center;
    color: var(--text-light);
    font-size: var(--font-size-sm);
    margin-bottom: var(--spacing-md);
}

.reaction-description {
    text-align: center;
}

/* =========================================
   Cell Comparison
   ========================================= */
.cell-comparison {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.cell-type {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
}

.cell-type h4 {
    margin-bottom: var(--spacing-md);
}

.cell-type ul {
    margin-left: var(--spacing-lg);
}

.cell-type li {
    position: relative;
    padding: var(--spacing-xs) 0;
    color: var(--text-secondary);
}

.cell-type li::before {
    content: '•';
    position: absolute;
    left: -1rem;
    color: var(--science-color);
}

/* =========================================
   Organelle Grid
   ========================================= */
.organelle-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.organelle-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    transition: transform var(--transition-fast);
}

.organelle-card:hover {
    transform: translateY(-5px);
}

.organelle-icon {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-md);
}

.organelle-card h4 {
    margin-bottom: var(--spacing-sm);
}

.organelle-card p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* =========================================
   DNA Info
   ========================================= */
.dna-info {
    display: flex;
    gap: var(--spacing-xl);
    align-items: center;
    flex-wrap: wrap;
    margin-top: var(--spacing-lg);
}

.dna-visual {
    font-size: 5rem;
    animation: spin 10s linear infinite;
}

@keyframes spin {
    from { transform: rotateY(0deg); }
    to { transform: rotateY(360deg); }
}

.dna-facts {
    flex: 1;
    min-width: 250px;
}

.dna-facts ul {
    margin-left: var(--spacing-lg);
}

.dna-facts li {
    position: relative;
    padding: var(--spacing-sm) 0;
    color: var(--text-secondary);
}

.dna-facts li::before {
    content: '→';
    position: absolute;
    left: -1.5rem;
    color: var(--science-color);
}

/* =========================================
   Technology Page Specific
   ========================================= */

/* IPO Model */
.ipo-model {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    margin: var(--spacing-xl) 0;
    flex-wrap: wrap;
}

.ipo-step {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    min-width: 150px;
}

.ipo-icon {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-sm);
}

.ipo-step h4 {
    margin-bottom: var(--spacing-sm);
}

.ipo-step p {
    font-size: var(--font-size-sm);
    margin: 0;
}

.ipo-arrow {
    font-size: var(--font-size-2xl);
    color: var(--primary-color);
}

/* Components Grid */
.components-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
}

.component-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
}

.component-icon {
    font-size: 2rem;
    margin-bottom: var(--spacing-md);
}

.component-card h4 {
    margin-bottom: var(--spacing-sm);
}

.component-card p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* Binary Converter */
.binary-demo {
    margin-top: var(--spacing-lg);
}

.binary-converter {
    display: flex;
    gap: var(--spacing-md);
    align-items: center;
    flex-wrap: wrap;
    margin: var(--spacing-lg) 0;
}

.binary-converter input {
    padding: var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    width: 200px;
}

.binary-converter input:focus {
    outline: none;
    border-color: var(--primary-color);
}

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

.result-label {
    font-weight: 500;
}

.result-value {
    font-family: 'Courier New', monospace;
    font-size: var(--font-size-lg);
    color: var(--primary-color);
    font-weight: 600;
}

.binary-examples {
    margin-top: var(--spacing-lg);
}

.binary-table {
    width: 100%;
    max-width: 300px;
    border-collapse: collapse;
}

.binary-table th,
.binary-table td {
    padding: var(--spacing-sm) var(--spacing-md);
    text-align: center;
    border: 1px solid var(--border-color);
}

.binary-table th {
    background: var(--bg-secondary);
    font-weight: 600;
}

/* Code Concepts */
.concept-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.code-concept {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
}

.code-concept h4 {
    margin-bottom: var(--spacing-sm);
}

.code-concept p {
    font-size: var(--font-size-sm);
    margin-bottom: var(--spacing-md);
}

.code-block {
    background: #1e1e1e;
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    overflow-x: auto;
}

.code-block code {
    display: block;
    color: #9cdcfe;
    font-family: 'Courier New', monospace;
    font-size: var(--font-size-sm);
    line-height: 1.5;
}

/* Languages Grid */
.languages-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.language-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    transition: transform var(--transition-fast);
}

.language-card:hover {
    transform: translateY(-5px);
}

.language-icon {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-md);
}

.language-card h4 {
    margin-bottom: var(--spacing-sm);
}

.language-card p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* Internet Visual */
.internet-visual {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    margin: var(--spacing-xl) 0;
    flex-wrap: wrap;
}

.network-node {
    background: var(--bg-tertiary);
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: var(--radius-lg);
    font-weight: 500;
    text-align: center;
}

.network-line {
    width: 40px;
    height: 3px;
    background: var(--primary-color);
}

/* Website Process */
.website-process {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-lg);
    justify-content: center;
    margin-top: var(--spacing-lg);
}

.process-step {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    min-width: 150px;
    flex: 1;
}

.step-number {
    width: 40px;
    height: 40px;
    background: var(--primary-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    margin: 0 auto var(--spacing-md);
}

.process-step h4 {
    margin-bottom: var(--spacing-sm);
    font-size: var(--font-size-base);
}

.process-step p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* Safety Tips */
.safety-card {
    border: 2px solid var(--science-color);
}

.safety-tips {
    display: grid;
    gap: var(--spacing-md);
}

.safety-tip {
    display: flex;
    gap: var(--spacing-md);
    align-items: flex-start;
    padding: var(--spacing-md);
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
}

.tip-icon {
    font-size: 1.5rem;
}

.safety-tip h4 {
    margin-bottom: var(--spacing-xs);
}

.safety-tip p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* =========================================
   Engineering Page Specific
   ========================================= */

/* Design Process */
.design-process {
    position: relative;
    padding-left: var(--spacing-xl);
}

.design-step {
    display: flex;
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
    position: relative;
}

.design-step::before {
    content: '';
    position: absolute;
    left: -1.25rem;
    top: 40px;
    bottom: -20px;
    width: 2px;
    background: var(--border-color);
}

.design-step:last-child::before {
    display: none;
}

.step-circle {
    width: 40px;
    height: 40px;
    background: var(--engineering-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    flex-shrink: 0;
    position: relative;
    z-index: 1;
}

.step-content {
    flex: 1;
}

.step-content h4 {
    margin-bottom: var(--spacing-sm);
}

.step-content p {
    margin: 0;
}

/* Engineer Types */
.engineer-types {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.engineer-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
    transition: transform var(--transition-fast);
}

.engineer-card:hover {
    transform: translateY(-5px);
}

.engineer-icon {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-md);
}

.engineer-card h4 {
    margin-bottom: var(--spacing-sm);
}

.engineer-card p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* Machines Grid */
.machines-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-xl);
}

.machine-card {
    background: var(--bg-primary);
    border: 1px solid var(--border-color);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
}

.machine-icon {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-md);
}

.machine-card h4 {
    margin-bottom: var(--spacing-sm);
}

.machine-card > p {
    margin-bottom: var(--spacing-md);
}

.machine-example {
    background: var(--bg-secondary);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    font-size: var(--font-size-sm);
}

.machine-diagram {
    margin-top: var(--spacing-md);
    text-align: center;
    font-family: monospace;
    color: var(--primary-color);
}

/* Forces Grid */
.forces-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.force-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
}

.force-visual {
    font-size: 1.5rem;
    margin-bottom: var(--spacing-md);
    font-family: monospace;
}

.force-card h4 {
    margin-bottom: var(--spacing-sm);
}

.force-card p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* Shapes Showcase */
.shapes-showcase {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.shape-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
}

.shape-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
    color: var(--engineering-color);
}

.shape-card h4 {
    margin-bottom: var(--spacing-sm);
}

.shape-card p {
    font-size: var(--font-size-sm);
    margin: 0;
}

/* Project Card */
.project-card {
    border: 2px dashed var(--engineering-color);
    background: rgba(245, 158, 11, 0.05);
}

.challenge-content {
    margin-top: var(--spacing-lg);
}

.challenge-details {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
}

.challenge-materials,
.challenge-goal {
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
}

.challenge-materials h5,
.challenge-goal h5,
.challenge-tips h5 {
    margin-bottom: var(--spacing-sm);
}

.challenge-materials ul,
.challenge-tips ul {
    margin-left: var(--spacing-lg);
}

.challenge-materials li,
.challenge-tips li {
    position: relative;
    padding: var(--spacing-xs) 0;
}

.challenge-materials li::before {
    content: '•';
    position: absolute;
    left: -1rem;
    color: var(--engineering-color);
}

.challenge-tips li::before {
    content: '→';
    position: absolute;
    left: -1.5rem;
    color: var(--engineering-color);
}

/* =========================================
   Mathematics Page Specific
   ========================================= */

/* Math Examples */
.math-example {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    margin: var(--spacing-lg) 0;
}

.math-example h4 {
    margin-bottom: var(--spacing-md);
}

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

.step {
    display: flex;
    gap: var(--spacing-lg);
    align-items: center;
    padding: var(--spacing-sm);
    background: var(--bg-primary);
    border-radius: var(--radius-md);
}

.step-equation {
    font-family: 'Courier New', monospace;
    font-weight: 600;
    min-width: 200px;
}

.step-explanation {
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
}

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

.step.final .step-explanation {
    color: rgba(255, 255, 255, 0.9);
}

/* PEMDAS Grid */
.pemdas-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(100px, 1fr));
    gap: var(--spacing-md);
    margin: var(--spacing-lg) 0;
}

.pemdas-item {
    background: var(--bg-secondary);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    text-align: center;
}

.pemdas-letter {
    display: block;
    font-size: var(--font-size-2xl);
    font-weight: 700;
    color: var(--mathematics-color);
}

.pemdas-word {
    display: block;
    font-weight: 500;
    margin: var(--spacing-xs) 0;
}

.pemdas-example {
    display: block;
    font-family: monospace;
    color: var(--text-light);
    font-size: var(--font-size-sm);
}

/* Practice Card */
.practice-card {
    background: var(--bg-secondary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    margin-top: var(--spacing-xl);
}

.practice-card h3 {
    margin-bottom: var(--spacing-lg);
}

.practice-problem {
    background: var(--bg-primary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    margin-bottom: var(--spacing-md);
}

.problem-text {
    margin-bottom: var(--spacing-md);
}

.answer-input {
    display: flex;
    gap: var(--spacing-md);
    align-items: center;
}

.practice-input {
    padding: var(--spacing-sm) var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    width: 120px;
}

.practice-input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.practice-feedback {
    margin-top: var(--spacing-sm);
    font-weight: 500;
}

.practice-feedback.correct {
    color: var(--science-color);
}

.practice-feedback.incorrect {
    color: var(--mathematics-color);
}

/* Shapes Formulas */
.shapes-formulas {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.shape-formula-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
}

.shape-visual {
    font-size: 3rem;
    color: var(--mathematics-color);
    margin-bottom: var(--spacing-md);
}

.shape-formula-card h4 {
    margin-bottom: var(--spacing-md);
}

.formula-group p {
    margin: var(--spacing-xs) 0;
    font-size: var(--font-size-sm);
}

/* Theorem Visual */
.theorem-visual {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-2xl);
    margin: var(--spacing-xl) 0;
    flex-wrap: wrap;
}

.triangle-diagram {
    position: relative;
    width: 150px;
    height: 120px;
}

.triangle-diagram::before {
    content: '';
    position: absolute;
    width: 0;
    height: 0;
    border-left: 75px solid transparent;
    border-right: 75px solid transparent;
    border-bottom: 120px solid var(--bg-tertiary);
}

.side-a, .side-b, .side-c {
    position: absolute;
    font-weight: 600;
    color: var(--mathematics-color);
}

.side-a { left: -20px; top: 50%; }
.side-b { right: -20px; bottom: -10px; }
.side-c { left: 50%; top: 50%; transform: translateX(-50%); }

/* Angles Grid */
.angles-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.angle-type {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    text-align: center;
}

.angle-visual {
    font-size: 2.5rem;
    margin-bottom: var(--spacing-md);
}

.angle-type h4 {
    margin-bottom: var(--spacing-sm);
}

.angle-type p {
    font-size: var(--font-size-sm);
    margin: 0;
    color: var(--text-secondary);
}

/* Stats Measures */
.stats-measures {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-lg);
}

.measure-card {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
}

.measure-card h4 {
    margin-bottom: var(--spacing-sm);
}

.measure-card > p {
    margin-bottom: var(--spacing-md);
    font-size: var(--font-size-sm);
}

/* Mean Calculator */
.mean-calculator {
    background: var(--bg-secondary);
    padding: var(--spacing-xl);
    border-radius: var(--radius-lg);
    margin-top: var(--spacing-lg);
}

.calc-input-group {
    display: flex;
    gap: var(--spacing-md);
    margin: var(--spacing-md) 0;
    flex-wrap: wrap;
}

.calc-input-group input {
    flex: 1;
    min-width: 200px;
    padding: var(--spacing-md);
    border: 2px solid var(--border-color);
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
}

.calc-input-group input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.calc-results {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
}

.result-item {
    background: var(--bg-primary);
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    text-align: center;
}

.result-item .result-label {
    display: block;
    font-size: var(--font-size-sm);
    color: var(--text-secondary);
    margin-bottom: var(--spacing-xs);
}

.result-item .result-value {
    display: block;
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--primary-color);
}

/* Probability Examples */
.probability-examples {
    background: var(--bg-secondary);
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    margin: var(--spacing-lg) 0;
}

.probability-examples h4 {
    margin-bottom: var(--spacing-md);
}

.probability-examples ul {
    margin-left: var(--spacing-lg);
}

.probability-examples li {
    position: relative;
    padding: var(--spacing-xs) 0;
}

.probability-examples li::before {
    content: '•';
    position: absolute;
    left: -1rem;
    color: var(--mathematics-color);
}

/* Probability Scale */
.probability-scale {
    margin-top: var(--spacing-xl);
}

.probability-scale h4 {
    text-align: center;
    margin-bottom: var(--spacing-lg);
}

.scale-visual {
    position: relative;
    padding: var(--spacing-2xl) 0;
}

.scale-bar {
    position: relative;
    height: 8px;
    background: linear-gradient(to right, var(--mathematics-color), var(--engineering-color), var(--science-color));
    border-radius: var(--radius-full);
}

.scale-point {
    position: absolute;
    top: -40px;
    transform: translateX(-50%);
    text-align: center;
    font-size: var(--font-size-sm);
    font-weight: 600;
}

.scale-point small {
    display: block;
    font-weight: 400;
    color: var(--text-light);
    margin-top: 50px;
}

/* =========================================
   Footer
   ========================================= */
.footer {
    background: var(--text-primary);
    color: white;
    padding: var(--spacing-3xl) 0 var(--spacing-xl);
}

.footer-content {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-2xl);
    margin-bottom: var(--spacing-2xl);
}

.footer-brand {
    max-width: 300px;
}

.footer-brand .logo-icon {
    font-size: 1.5rem;
    margin-right: var(--spacing-sm);
}

.footer-brand .logo-text {
    font-size: var(--font-size-xl);
    font-weight: 700;
}

.footer-brand p {
    margin-top: var(--spacing-md);
    color: var(--text-light);
    font-size: var(--font-size-sm);
}

.footer-links h4,
.footer-contact h4 {
    margin-bottom: var(--spacing-md);
    font-size: var(--font-size-base);
}

.footer-links ul,
.footer-contact ul {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.footer-links a,
.footer-contact a {
    color: var(--text-light);
    font-size: var(--font-size-sm);
    transition: color var(--transition-fast);
}

.footer-links a:hover,
.footer-contact a:hover {
    color: white;
}

.footer-bottom {
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    padding-top: var(--spacing-xl);
    text-align: center;
    color: var(--text-light);
    font-size: var(--font-size-sm);
}

/* =========================================
   Responsive Design
   ========================================= */
@media (max-width: 768px) {
    .nav-toggle {
        display: flex;
    }
    
    .nav-menu {
        position: fixed;
        top: 60px;
        left: 0;
        right: 0;
        background: var(--bg-primary);
        flex-direction: column;
        padding: var(--spacing-lg);
        gap: 0;
        border-bottom: 1px solid var(--border-color);
        transform: translateY(-100%);
        opacity: 0;
        visibility: hidden;
        transition: all var(--transition-base);
    }
    
    .nav-menu.active {
        transform: translateY(0);
        opacity: 1;
        visibility: visible;
    }
    
    .nav-link {
        padding: var(--spacing-md);
        border-bottom: 1px solid var(--border-color);
    }
    
    .hero-title {
        font-size: var(--font-size-2xl);
    }
    
    .hero-buttons {
        flex-direction: column;
    }
    
    .btn {
        width: 100%;
    }
    
    .topic-nav {
        flex-direction: column;
    }
    
    .topic-btn {
        width: 100%;
    }
    
    .ipo-model {
        flex-direction: column;
    }
    
    .ipo-arrow {
        transform: rotate(90deg);
    }
    
    .network-line {
        width: 3px;
        height: 20px;
    }
    
    .internet-visual {
        flex-direction: column;
    }
    
    .step {
        flex-direction: column;
        text-align: center;
    }
    
    .step-equation {
        min-width: auto;
    }
    
    .design-process {
        padding-left: var(--spacing-md);
    }
    
    .design-step {
        flex-direction: column;
    }
    
    .design-step::before {
        left: 15px;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 var(--spacing-md);
    }
    
    .lesson-card {
        padding: var(--spacing-md);
    }
    
    .page-icon {
        font-size: 3rem;
    }
    
    .page-header h1 {
        font-size: var(--font-size-2xl);
    }
    
    .binary-converter {
        flex-direction: column;
    }
    
    .binary-converter input {
        width: 100%;
    }
}

/* Print Styles */
@media print {
    .navbar,
    .nav-toggle,
    .hero-buttons,
    .quiz-card,
    .practice-card,
    .fact-dots,
    .footer {
        display: none !important;
    }
    
    body {
        font-size: 12pt;
        color: black;
    }
    
    .lesson-card {
        break-inside: avoid;
        border: 1px solid #ccc;
    }
}