/* Import Google Fonts */
@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@400;600;700;800&family=Inter:wght@400;500;600&display=swap');

/* ============================
   CSS Variables & Design Tokens
   ============================ */
:root {
    /* Primary Colors */
    --primary-purple: #7c3aed;
    --primary-blue: #3b82f6;
    --primary-green: #10b981;
    --primary-orange: #f59e0b;
    --primary-pink: #ec4899;
    
    /* Gradients */
    --gradient-primary: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --gradient-success: linear-gradient(135deg, #10b981 0%, #059669 100%);
    --gradient-warning: linear-gradient(135deg, #f59e0b 0%, #d97706 100%);
    --gradient-code: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%);
    --gradient-hero: linear-gradient(135deg, #667eea 0%, #764ba2 50%, #f093fb 100%);
    
    /* Neutral Colors */
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --text-light: #9ca3af;
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;
    --border-light: #e5e7eb;
    --border-medium: #d1d5db;
    
    /* 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);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    --shadow-glow: 0 0 20px rgba(102, 126, 234, 0.4);
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    --radius-full: 9999px;
    
    /* Transitions */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 300ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 500ms cubic-bezier(0.4, 0, 0.2, 1);
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    overflow-x: hidden;
}

/* ============================
   Typography
   ============================ */
h1, h2, h3, h4, h5, h6 {
    font-family: 'Poppins', sans-serif;
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-md);
}

h1 {
    font-size: 2.5rem;
    font-weight: 800;
}

h2 {
    font-size: 2rem;
    font-weight: 700;
}

h3 {
    font-size: 1.5rem;
}

p {
    margin-bottom: var(--spacing-md);
}

code {
    font-family: 'Courier New', Courier, monospace;
    background: rgba(79, 70, 229, 0.1);
    padding: 0.2rem 0.4rem;
    border-radius: 0.25rem;
    font-size: 0.9em;
    color: var(--primary-purple);
}

/* ============================
   Layout Components
   ============================ */

/* Main Container */
.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: var(--spacing-xl);
}

/* Header */
.header {
    background: var(--gradient-hero);
    color: white;
    padding: var(--spacing-xl) 0;
    box-shadow: var(--shadow-lg);
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(10px);
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 var(--spacing-xl);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

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

.logo-icon {
    font-size: 2.5rem;
}

.logo-text h1 {
    font-size: 1.75rem;
    margin: 0;
    font-weight: 800;
}

.logo-text p {
    font-size: 0.9rem;
    margin: 0;
    opacity: 0.9;
}

.header-stats {
    display: flex;
    gap: var(--spacing-lg);
}

.stat-item {
    text-align: center;
    background: rgba(255, 255, 255, 0.2);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    backdrop-filter: blur(10px);
}

.stat-value {
    font-size: 1.5rem;
    font-weight: 700;
    display: block;
}

.stat-label {
    font-size: 0.8rem;
    opacity: 0.9;
}

/* Progress Bar */
.progress-section {
    background: white;
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
    margin-bottom: var(--spacing-xl);
}

.progress-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-md);
}

.progress-bar {
    width: 100%;
    height: 1.25rem;
    background: var(--bg-tertiary);
    border-radius: var(--radius-full);
    overflow: hidden;
    position: relative;
}

.progress-fill {
    height: 100%;
    background: var(--gradient-success);
    border-radius: var(--radius-full);
    transition: width var(--transition-slow);
    position: relative;
    overflow: hidden;
}

.progress-fill::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background: linear-gradient(
        90deg,
        transparent,
        rgba(255, 255, 255, 0.3),
        transparent
    );
    animation: shimmer 2s infinite;
}

@keyframes shimmer {
    0% { transform: translateX(-100%); }
    100% { transform: translateX(100%); }
}

/* Main Content Grid */
.main-content {
    display: grid;
    grid-template-columns: 300px 1fr;
    gap: var(--spacing-xl);
    max-width: 1400px;
    margin: 0 auto;
    padding: 0 var(--spacing-xl);
}

/* Sidebar */
.sidebar {
    position: sticky;
    top: 120px;
    height: fit-content;
}

.lesson-nav {
    background: white;
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
}

.lesson-nav h3 {
    font-size: 1.2rem;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.lesson-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
    margin-bottom: var(--spacing-xs);
}

.lesson-item:hover {
    background: var(--bg-secondary);
    transform: translateX(4px);
}

.lesson-item.active {
    background: var(--gradient-primary);
    color: white;
    box-shadow: var(--shadow-md);
}

.lesson-icon {
    width: 32px;
    height: 32px;
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
    background: var(--bg-tertiary);
}

.lesson-item.active .lesson-icon {
    background: rgba(255, 255, 255, 0.2);
}

.lesson-item.completed .lesson-icon {
    background: var(--gradient-success);
    color: white;
}

.lesson-details {
    flex: 1;
}

.lesson-title {
    font-weight: 600;
    font-size: 0.95rem;
}

.lesson-subtitle {
    font-size: 0.8rem;
    opacity: 0.7;
}

/* Locked Lessons */
.lesson-item.locked {
    opacity: 0.5;
    cursor: not-allowed;
    pointer-events: none;
}

.lesson-item.locked::after {
    content: '🔒';
    margin-left: auto;
    font-size: 1rem;
}

.lesson-item.locked:hover {
    background: transparent;
    transform: none;
}

/* Main Lesson Area */
.lesson-area {
    background: white;
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    box-shadow: var(--shadow-xl);
    min-height: 600px;
}

/* Lesson Card */
.lesson-card {
    display: none;
    animation: fadeInUp var(--transition-base);
}

.lesson-card.active {
    display: block;
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.lesson-header {
    border-bottom: 2px solid var(--border-light);
    padding-bottom: var(--spacing-lg);
    margin-bottom: var(--spacing-xl);
}

.lesson-badge {
    display: inline-block;
    background: var(--gradient-primary);
    color: white;
    padding: 0.3rem 0.8rem;
    border-radius: var(--radius-full);
    font-size: 0.85rem;
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
}

/* ROBie Mascot */
.robie-container {
    position: fixed;
    bottom: var(--spacing-xl);
    right: var(--spacing-xl);
    z-index: 50;
    animation: float 3s ease-in-out infinite;
}

@keyframes float {
    0%, 100% { transform: translateY(0px); }
    50% { transform: translateY(-10px); }
}

.robie-image {
    width: 120px;
    height: 120px;
    object-fit: contain;
    filter: drop-shadow(0 10px 20px rgba(0, 0, 0, 0.15));
    transition: all var(--transition-base);
}

.robie-container:hover .robie-image {
    transform: scale(1.1);
}

.robie-speech {
    position: absolute;
    bottom: 100%;
    right: 0;
    background: white;
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    max-width: 200px;
    margin-bottom: var(--spacing-sm);
    opacity: 0;
    transform: translateY(10px);
    transition: all var(--transition-base);
    pointer-events: none;
}

.robie-speech.visible {
    opacity: 1;
    transform: translateY(0);
}

.robie-speech::after {
    content: '';
    position: absolute;
    bottom: -8px;
    right: 20px;
    width: 0;
    height: 0;
    border-left: 8px solid transparent;
    border-right: 8px solid transparent;
    border-top: 8px solid white;
}

/* Code Block */
.code-block {
    background: linear-gradient(135deg, #1e1e2e 0%, #2a2a3e 100%);
    color: #e6e6e6;
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    font-family: 'Courier New', Courier, monospace;
    margin: var(--spacing-lg) 0;
    overflow-x: auto;
    position: relative;
    box-shadow: var(--shadow-lg);
}

.code-block::before {
    content: 'Python';
    position: absolute;
    top: var(--spacing-sm);
    right: var(--spacing-md);
    font-size: 0.7rem;
    text-transform: uppercase;
    opacity: 0.5;
    font-weight: 600;
}

.code-line {
    margin: 0.5rem 0;
}

.keyword { color: #ff79c6; }
.string { color: #50fa7b; }
.number { color: #bd93f9; }
.comment { color: #6272a4; }
.function { color: #8be9fd; }

/* Interactive Code Editor */
.code-editor {
    background: #1e1e2e;
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    margin: var(--spacing-lg) 0;
    box-shadow: var(--shadow-lg);
}

.code-editor-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-sm);
    padding-bottom: var(--spacing-sm);
    border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.editor-title {
    color: #e6e6e6;
    font-size: 0.9rem;
    font-weight: 600;
}

.code-input {
    width: 100%;
    background: #2a2a3e;
    color: #e6e6e6;
    border: 2px solid #3a3a4e;
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    font-family: 'Courier New', Courier, monospace;
    font-size: 1rem;
    resize: vertical;
    min-height: 100px;
    transition: border-color var(--transition-base);
}

.code-input:focus {
    outline: none;
    border-color: var(--primary-blue);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.2);
}

.code-output {
    background: #0d0d17;
    color: #50fa7b;
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    margin-top: var(--spacing-sm);
    font-family: 'Courier New', Courier, monospace;
    min-height: 60px;
    display: none;
}

.code-output.visible {
    display: block;
}

/* Quiz Options */
.quiz-options {
    display: grid;
    gap: var(--spacing-md);
    margin: var(--spacing-lg) 0;
}

.option-btn {
    background: white;
    border: 2px solid var(--border-medium);
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-base);
    text-align: left;
    font-size: 1rem;
    font-family: 'Inter', sans-serif;
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

.option-btn:hover {
    border-color: var(--primary-blue);
    background: rgba(59, 130, 246, 0.05);
    transform: translateX(4px);
}

.option-btn.correct {
    border-color: var(--primary-green);
    background: rgba(16, 185, 129, 0.1);
    animation: correctPulse var(--transition-base);
}

.option-btn.wrong {
    border-color: #ef4444;
    background: rgba(239, 68, 68, 0.1);
    animation: shake 0.5s;
}

.option-btn:disabled {
    cursor: not-allowed;
    opacity: 0.6;
}

@keyframes correctPulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.02); }
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

.option-letter {
    width: 32px;
    height: 32px;
    border-radius: var(--radius-sm);
    background: var(--bg-tertiary);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 0.9rem;
}

.option-btn.correct .option-letter {
    background: var(--primary-green);
    color: white;
}

.option-btn.wrong .option-letter {
    background: #ef4444;
    color: white;
}

/* Buttons */
.btn {
    padding: var(--spacing-sm) var(--spacing-xl);
    border: none;
    border-radius: var(--radius-md);
    font-family: 'Poppins', sans-serif;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: all var(--transition-base);
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-sm);
    position: relative;
    overflow: hidden;
}

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

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

.btn-primary:active {
    transform: translateY(0);
}

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

.btn-run {
    background: var(--gradient-code);
    color: white;
}

.btn-disabled {
    opacity: 0.5;
    cursor: not-allowed;
    pointer-events: none;
}

/* Action Buttons */
.action-buttons {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: var(--spacing-xl);
    padding-top: var(--spacing-xl);
    border-top: 2px solid var(--border-light);
}

/* Celebration Overlay */
.celebration-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.8);
    display: none;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    animation: fadeIn var(--transition-base);
}

.celebration-overlay.visible {
    display: flex;
}

.celebration-content {
    background: white;
    padding: var(--spacing-2xl);
    border-radius: var(--radius-xl);
    text-align: center;
    max-width: 500px;
    animation: bounceIn var(--transition-slow);
}

@keyframes bounceIn {
    0% {
        opacity: 0;
        transform: scale(0.3);
    }
    50% {
        opacity: 1;
        transform: scale(1.05);
    }
    70% {
        transform: scale(0.9);
    }
    100% {
        transform: scale(1);
    }
}

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

.celebration-icon {
    font-size: 5rem;
    margin-bottom: var(--spacing-md);
    animation: rotate360 var(--transition-slow);
}

@keyframes rotate360 {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

/* Utility Classes */
.hidden {
    display: none !important;
}

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

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

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

/* Responsive Design */
@media (max-width: 1024px) {
    .main-content {
        grid-template-columns: 1fr;
    }
    
    .sidebar {
        position: static;
    }
    
    .lesson-nav {
        margin-bottom: var(--spacing-xl);
    }
}

@media (max-width: 768px) {
    .header-stats {
        display: none;
    }
    
    .logo-text h1 {
        font-size: 1.25rem;
    }
    
    .lesson-area {
        padding: var(--spacing-lg);
    }
    
    .robie-container {
        bottom: var(--spacing-md);
        right: var(--spacing-md);
    }
    
    .robie-image {
        width: 80px;
        height: 80px;
    }
}