/* ===================== RESET & VARIABLES ===================== */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg-dark: #0f0f0f;
    --bg-card: #1a1a1a;
    --bg-input: #252525;
    --bg-hover: #2a2a2a;
    --text-primary: #ffffff;
    --text-secondary: #a0a0a0;
    --text-muted: #666666;
    --accent: #3b82f6;
    --accent-light: #60a5fa;
    --success: #22c55e;
    --error: #ef4444;
    --warning: #f59e0b;
    --border: #333333;
    --code-bg: #0d0d0d;
    --code-keyword: #ff79c6;
    --code-string: #f1fa8c;
    --code-number: #bd93f9;
    --code-comment: #6272a4;
    --code-method: #50fa7b;
    --code-type: #8be9fd;
    --radius: 8px;
    --radius-lg: 12px;
    --transition: 0.2s ease;
}

html {
    font-size: 16px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: var(--bg-dark);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    overflow-x: hidden;
}

/* ===================== LAYOUT ===================== */
#app {
    display: flex;
    min-height: 100vh;
}

/* ===================== SIDEBAR ===================== */
#sidebar {
    width: 260px;
    background: var(--bg-card);
    border-right: 1px solid var(--border);
    position: fixed;
    height: 100vh;
    overflow-y: auto;
    z-index: 100;
    display: flex;
    flex-direction: column;
}

.sidebar-toggle {
    display: none;
    position: fixed;
    top: 12px;
    left: 12px;
    z-index: 200;
    background: var(--bg-card);
    border: 1px solid var(--border);
    color: var(--text-primary);
    font-size: 18px;
    padding: 10px 14px;
    border-radius: var(--radius);
    cursor: pointer;
}

.logo {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 20px;
    border-bottom: 1px solid var(--border);
}

.logo-icon {
    font-size: 28px;
}

.logo h2 {
    font-size: 18px;
    font-weight: 700;
    color: var(--accent);
}

.logo-sub {
    font-size: 11px;
    color: var(--text-muted);
    display: block;
}

.progress-overall {
    padding: 16px 20px;
    border-bottom: 1px solid var(--border);
}

.progress-bar {
    height: 6px;
    background: var(--bg-input);
    border-radius: 3px;
    overflow: hidden;
    margin-bottom: 6px;
}

.progress-bar.large {
    height: 10px;
    border-radius: 5px;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent), var(--success));
    border-radius: inherit;
    transition: width 0.4s ease;
}

#progress-text {
    font-size: 11px;
    color: var(--text-muted);
}

#module-list {
    flex: 1;
    padding: 12px;
    overflow-y: auto;
}

.module-item {
    display: flex;
    flex-direction: column;
    padding: 12px 14px;
    margin-bottom: 4px;
    border-radius: var(--radius);
    cursor: pointer;
    transition: all var(--transition);
    border: 1px solid transparent;
}

.module-item:hover {
    background: var(--bg-hover);
}

.module-item.active {
    background: var(--accent);
    color: var(--bg-dark);
}

.module-item.active .module-name {
    color: var(--bg-dark);
}

.module-item.active .progress-fill {
    background: var(--bg-dark);
}

.module-item.highlight {
    border-color: var(--warning);
}

.module-item-header {
    display: flex;
    align-items: center;
    gap: 10px;
}

.module-icon {
    font-size: 18px;
}

.module-name {
    flex: 1;
    font-size: 13px;
    font-weight: 500;
    color: var(--text-primary);
}

.star-badge {
    color: var(--warning);
    font-size: 14px;
}

.module-progress {
    margin-top: 8px;
}

.module-progress .progress-bar {
    height: 3px;
}

/* ===================== MAIN CONTENT ===================== */
main {
    flex: 1;
    margin-left: 260px;
    padding: 32px 40px;
    max-width: 1000px;
    min-width: 0;
    overflow-x: hidden;
}

/* ===================== WELCOME PAGE ===================== */
#welcome-page {
    display: block;
}

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

.welcome-title {
    font-size: 32px;
    font-weight: 700;
    text-align: center;
    margin-bottom: 8px;
    background: linear-gradient(135deg, var(--accent), var(--accent-light));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.welcome-subtitle {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 32px;
}

.overall-progress-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 24px;
    text-align: center;
    margin-bottom: 40px;
}

.overall-progress-card h3 {
    font-size: 14px;
    color: var(--text-secondary);
    margin-bottom: 12px;
}

.section-title {
    font-size: 18px;
    margin-bottom: 20px;
    color: var(--text-primary);
}

.learning-stages {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 12px;
    margin-bottom: 40px;
}

.stage-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 20px 12px;
    text-align: center;
}

.stage-icon {
    font-size: 28px;
    display: block;
    margin-bottom: 8px;
}

.stage-card h4 {
    font-size: 13px;
    margin-bottom: 4px;
}

.stage-card p {
    font-size: 11px;
    color: var(--text-muted);
}

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

.quick-start h3 {
    margin-bottom: 16px;
    color: var(--text-secondary);
}

.quick-start-buttons {
    display: flex;
    gap: 12px;
    justify-content: center;
    margin-bottom: 12px;
}

.note {
    font-size: 12px;
    color: var(--text-muted);
}

/* ===================== BUTTONS ===================== */
.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 20px;
    border-radius: var(--radius);
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition);
    border: 1px solid transparent;
}

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

.btn-primary:hover {
    background: var(--accent-light);
}

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

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

.btn-outline {
    background: transparent;
    color: var(--text-primary);
    border-color: var(--border);
}

.btn-outline:hover {
    background: var(--bg-hover);
}

.btn-large {
    padding: 14px 28px;
    font-size: 15px;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* ===================== MODULE VIEW ===================== */
#module-view {
    display: none;
}

.module-header {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-bottom: 24px;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--border);
}

.module-header-title {
    display: flex;
    align-items: center;
    gap: 12px;
}

.module-header-title span {
    font-size: 28px;
}

#module-title {
    font-size: 24px;
    font-weight: 600;
}

.back-btn {
    background: var(--bg-input);
    border: 1px solid var(--border);
    color: var(--text-secondary);
    padding: 8px 14px;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 13px;
    transition: all var(--transition);
}

.back-btn:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

/* ===================== TABS ===================== */
.tabs {
    display: flex;
    gap: 6px;
    margin-bottom: 24px;
    flex-wrap: wrap;
}

.tab-btn {
    display: flex;
    align-items: center;
    gap: 6px;
    background: var(--bg-input);
    border: 1px solid var(--border);
    color: var(--text-secondary);
    padding: 10px 16px;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 13px;
    transition: all var(--transition);
}

.tab-btn:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.tab-btn.active {
    background: var(--accent);
    border-color: var(--accent);
    color: white;
}

.tab-icon {
    font-size: 14px;
}

.tab-complete {
    color: var(--success);
    font-size: 12px;
}

.tab-btn.active .tab-complete {
    color: white;
}

/* ===================== TAB CONTENT ===================== */
.tab-content, #module-content {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 28px;
    min-height: 400px;
}

.loading {
    text-align: center;
    color: var(--text-muted);
    padding: 40px;
}

/* ===================== CONCEPT SECTION ===================== */
.concept-section {
    max-width: 760px;
}

.concept-title {
    font-size: 22px;
    font-weight: 600;
    margin-bottom: 16px;
}

.concept-text {
    color: var(--text-secondary);
    margin-bottom: 16px;
    line-height: 1.7;
}

.concept-analogy {
    background: rgba(59, 130, 246, 0.1);
    border-left: 3px solid var(--accent);
    padding: 16px 20px;
    margin: 20px 0;
    border-radius: 0 var(--radius) var(--radius) 0;
}

.concept-analogy h4 {
    color: var(--accent);
    font-size: 13px;
    margin-bottom: 6px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.concept-list {
    margin: 16px 0;
    padding-left: 20px;
}

.concept-list li {
    margin-bottom: 8px;
    color: var(--text-secondary);
}

.concept-list li strong {
    color: var(--text-primary);
}

.key-point {
    background: var(--bg-input);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 16px;
    margin: 20px 0;
}

.key-point h4 {
    color: var(--warning);
    font-size: 13px;
    margin-bottom: 8px;
}

.info-box {
    background: var(--bg-input);
    border-radius: var(--radius);
    padding: 16px;
    margin: 12px 0;
}

.warning-box {
    background: rgba(245, 158, 11, 0.1);
    border: 1px solid var(--warning);
    border-radius: var(--radius);
    padding: 12px 16px;
    color: var(--warning);
}

.visual-box {
    background: var(--bg-input);
    border-radius: var(--radius);
    padding: 16px;
    margin: 12px 0;
}

.tab-content-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 16px;
    margin: 16px 0;
}

/* ===================== COMPARISON TABLE ===================== */
.comparison-table {
    width: 100%;
    border-collapse: collapse;
    margin: 16px 0;
    font-size: 13px;
}

.comparison-table th,
.comparison-table td {
    padding: 10px 12px;
    text-align: left;
    border: 1px solid var(--border);
}

.comparison-table th {
    background: var(--bg-input);
    font-weight: 600;
    color: var(--text-primary);
}

.comparison-table td {
    background: var(--bg-card);
    color: var(--text-secondary);
}

.comparison-table code {
    background: var(--code-bg);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: 'Monaco', 'Consolas', monospace;
    font-size: 12px;
    color: var(--accent-light);
}

/* ===================== CODE BLOCKS ===================== */
.code-block {
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    overflow: hidden;
    margin: 16px 0;
}

.code-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: var(--bg-input);
    padding: 8px 14px;
    font-size: 12px;
    color: var(--text-muted);
    border-bottom: 1px solid var(--border);
}

.code-content {
    padding: 14px;
    overflow-x: auto;
    font-family: 'Monaco', 'Menlo', 'Consolas', monospace;
    font-size: 13px;
    line-height: 1.5;
}

.code-content pre {
    margin: 0;
    white-space: pre;
}

/* Code syntax colors - class names */
.keyword { color: var(--code-keyword); }
.type { color: var(--code-type); }
.method { color: var(--code-method); }
.string { color: var(--code-string); }
.number { color: var(--code-number); }
.comment { color: var(--code-comment); font-style: italic; }

/* Code line display */
.code-line {
    display: flex;
    min-height: 22px;
    padding: 0 4px;
}

.code-line:hover {
    background: rgba(255, 255, 255, 0.03);
}

.code-line.highlight-line {
    background: rgba(59, 130, 246, 0.15);
    border-left: 3px solid var(--accent);
    margin-left: -3px;
}

.code-line.error-line {
    background: rgba(239, 68, 68, 0.15);
    border-left: 3px solid var(--error);
}

.line-number {
    color: var(--text-muted);
    min-width: 32px;
    text-align: right;
    padding-right: 12px;
    user-select: none;
    font-size: 12px;
}

.line-code {
    flex: 1;
    white-space: pre;
}

/* ===================== VISUALIZER ===================== */
.simulation-container {
    padding: 20px 0;
}

.controls {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
    margin-bottom: 20px;
}

.controls input,
.controls select {
    background: var(--bg-input);
    border: 1px solid var(--border);
    color: var(--text-primary);
    padding: 10px 14px;
    border-radius: var(--radius);
    font-size: 14px;
}

.controls input:focus,
.controls select:focus {
    outline: none;
    border-color: var(--accent);
}

.visualizer-container {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    margin: 20px 0;
}

.visualizer-canvas {
    min-height: 200px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 16px;
}

.viz-btn {
    background: var(--bg-input);
    border: 1px solid var(--border);
    color: var(--text-primary);
    padding: 10px 18px;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 13px;
    transition: all var(--transition);
}

.viz-btn:hover:not(:disabled) {
    background: var(--accent);
    border-color: var(--accent);
    color: white;
}

.viz-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Stack/Queue elements */
.stack-element,
.queue-element {
    background: var(--accent);
    color: white;
    padding: 12px 28px;
    border-radius: var(--radius);
    font-weight: 600;
    font-size: 16px;
    min-width: 80px;
    text-align: center;
    animation: fadeSlideIn 0.3s ease;
}

@keyframes fadeSlideIn {
    from {
        opacity: 0;
        transform: translateY(-16px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.viz-info {
    background: var(--bg-input);
    padding: 14px;
    border-radius: var(--radius);
    margin-top: 16px;
    font-size: 13px;
    color: var(--text-secondary);
}

.viz-info code {
    background: var(--code-bg);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: monospace;
    color: var(--accent-light);
}

/* ===================== MEMORY ANALYSIS ===================== */
.memory-analysis {
    display: grid;
    grid-template-columns: 1.2fr 1fr;
    gap: 20px;
    margin: 20px 0;
}

.memory-code {
    min-width: 0;
}

.memory-state {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 16px;
}

.memory-state h4 {
    color: var(--accent);
    font-size: 13px;
    margin-bottom: 12px;
}

.memory-var {
    display: flex;
    justify-content: space-between;
    padding: 8px 10px;
    background: var(--bg-input);
    border-radius: 4px;
    margin-bottom: 6px;
    font-family: monospace;
    font-size: 13px;
}

.memory-var-name {
    color: var(--code-method);
}

.memory-var-value {
    color: var(--code-number);
}

.memory-array {
    display: flex;
    gap: 4px;
    margin-top: 12px;
}

.memory-cell {
    background: var(--bg-input);
    border: 1px solid var(--border);
    padding: 10px 14px;
    text-align: center;
    position: relative;
    border-radius: 4px;
    min-width: 36px;
    font-family: monospace;
}

.memory-cell.active {
    border-color: var(--accent);
    background: rgba(59, 130, 246, 0.15);
}

.memory-index {
    font-size: 10px;
    color: var(--text-muted);
    position: absolute;
    bottom: -16px;
    left: 50%;
    transform: translateX(-50%);
}

.step-controls {
    display: flex;
    gap: 12px;
    margin-top: 20px;
    align-items: center;
}

.step-indicator {
    color: var(--text-secondary);
    font-size: 13px;
}

/* ===================== QUIZ ===================== */
.quiz-container {
    max-width: 680px;
}

.quiz-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    padding-bottom: 12px;
    border-bottom: 1px solid var(--border);
}

.quiz-progress {
    font-size: 13px;
    color: var(--text-secondary);
}

.quiz-score {
    font-size: 13px;
    color: var(--success);
}

.quiz-question {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 20px;
    margin-bottom: 20px;
}

.quiz-question h3 {
    font-size: 15px;
    margin-bottom: 16px;
    line-height: 1.5;
    white-space: pre-wrap;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.quiz-option {
    display: flex;
    align-items: center;
    gap: 12px;
    background: var(--bg-input);
    border: 2px solid var(--border);
    border-radius: var(--radius);
    padding: 14px;
    cursor: pointer;
    transition: all var(--transition);
    font-size: 14px;
}

.quiz-option:hover:not(.disabled) {
    border-color: var(--accent);
    background: rgba(59, 130, 246, 0.05);
}

.quiz-option.selected {
    border-color: var(--accent);
    background: rgba(59, 130, 246, 0.1);
}

.quiz-option.correct {
    border-color: var(--success);
    background: rgba(34, 197, 94, 0.1);
}

.quiz-option.wrong {
    border-color: var(--error);
    background: rgba(239, 68, 68, 0.1);
}

.quiz-option.disabled {
    cursor: not-allowed;
    opacity: 0.7;
}

.quiz-option-marker {
    width: 22px;
    height: 22px;
    border: 2px solid var(--border);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 11px;
    font-weight: 600;
    flex-shrink: 0;
}

.quiz-option.selected .quiz-option-marker {
    border-color: var(--accent);
    background: var(--accent);
    color: white;
}

.quiz-option.correct .quiz-option-marker {
    border-color: var(--success);
    background: var(--success);
    color: white;
}

.quiz-option.wrong .quiz-option-marker {
    border-color: var(--error);
    background: var(--error);
    color: white;
}

.quiz-feedback {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 16px;
    margin-top: 12px;
    display: none;
}

.quiz-feedback.show {
    display: block;
}

.quiz-feedback.correct {
    border-color: var(--success);
}

.quiz-feedback.wrong {
    border-color: var(--error);
}

.quiz-feedback h4 {
    margin-bottom: 6px;
    font-size: 14px;
}

.quiz-feedback.correct h4 { color: var(--success); }
.quiz-feedback.wrong h4 { color: var(--error); }

.quiz-feedback p {
    color: var(--text-secondary);
    font-size: 13px;
}

.quiz-actions {
    display: flex;
    gap: 10px;
    margin-top: 16px;
}

.quiz-btn {
    background: var(--accent);
    border: none;
    color: white;
    padding: 10px 20px;
    border-radius: var(--radius);
    cursor: pointer;
    font-size: 13px;
    font-weight: 500;
    transition: all var(--transition);
}

.quiz-btn:hover {
    background: var(--accent-light);
}

.quiz-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.quiz-btn.secondary {
    background: var(--bg-input);
    color: var(--text-primary);
    border: 1px solid var(--border);
}

/* Fill in blank */
.fill-blank-template {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 16px;
    font-family: monospace;
    font-size: 14px;
    line-height: 1.8;
    white-space: pre-wrap;
    margin-bottom: 16px;
}

.blank-input {
    background: var(--bg-input);
    border: 2px solid var(--border);
    border-radius: 4px;
    padding: 4px 8px;
    font-family: monospace;
    font-size: 13px;
    color: var(--text-primary);
    min-width: 60px;
    text-align: center;
}

.blank-input:focus {
    outline: none;
    border-color: var(--accent);
}

.blank-input.correct {
    border-color: var(--success);
    background: rgba(34, 197, 94, 0.1);
}

.blank-input.wrong {
    border-color: var(--error);
    background: rgba(239, 68, 68, 0.1);
}

/* Quiz Results */
.quiz-results {
    text-align: center;
    padding: 32px;
}

.quiz-results h3 {
    font-size: 20px;
    margin-bottom: 12px;
}

.quiz-results .score-display {
    font-size: 48px;
    font-weight: 700;
    color: var(--accent);
    margin: 16px 0;
}

.quiz-results .score-text {
    color: var(--text-secondary);
    margin-bottom: 24px;
}

/* ===================== BUG FINDER ===================== */
.bug-finder {
    max-width: 720px;
}

.bug-instruction {
    background: rgba(245, 158, 11, 0.15);
    border: 1px solid var(--warning);
    color: var(--warning);
    padding: 12px 16px;
    border-radius: var(--radius);
    margin-bottom: 16px;
    font-size: 13px;
}

.bug-code {
    margin: 16px 0;
}

.bug-code .code-line {
    cursor: pointer;
    padding: 2px 8px;
    border-radius: 2px;
}

.bug-code .code-line:hover {
    background: rgba(255, 255, 255, 0.05);
}

.bug-code .code-line.selected {
    background: rgba(239, 68, 68, 0.15);
    border-left: 3px solid var(--error);
}

.bug-hint {
    background: var(--bg-dark);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 14px;
    margin-top: 12px;
    font-size: 13px;
}

/* ===================== LINKED LIST ===================== */
.linked-list-viz {
    display: flex;
    align-items: center;
    gap: 4px;
    padding: 16px 0;
    overflow-x: auto;
}

.ll-node {
    display: flex;
    align-items: center;
}

.ll-node-content {
    background: var(--accent);
    color: white;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    border-radius: var(--radius) 0 0 var(--radius);
}

.ll-node-pointer {
    background: var(--bg-input);
    width: 24px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 0 var(--radius) var(--radius) 0;
}

.ll-arrow {
    color: var(--text-muted);
    font-size: 18px;
    margin: 0 4px;
}

.ll-null {
    color: var(--error);
    font-family: monospace;
    font-weight: 600;
}

.ll-pointer-label {
    font-size: 11px;
    color: var(--warning);
    position: absolute;
    top: -18px;
    left: 50%;
    transform: translateX(-50%);
}

/* ===================== SORTING VIZ ===================== */
.sorting-bars {
    display: flex;
    align-items: flex-end;
    gap: 4px;
    height: 200px;
    padding: 20px;
    background: var(--bg-dark);
    border-radius: var(--radius);
}

.sorting-bar {
    flex: 1;
    background: var(--accent);
    border-radius: 4px 4px 0 0;
    display: flex;
    align-items: flex-end;
    justify-content: center;
    padding-bottom: 4px;
    font-size: 11px;
    color: white;
    font-weight: 600;
    transition: all 0.2s;
    min-width: 24px;
}

.sorting-bar.comparing {
    background: var(--warning);
}

.sorting-bar.swapping {
    background: var(--error);
}

.sorting-bar.sorted {
    background: var(--success);
}

/* ===================== FADE IN ANIMATION ===================== */
.fade-in {
    animation: fadeIn 0.3s ease;
}

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

/* ===================== RESPONSIVE ===================== */

/* Sidebar overlay backdrop */
.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.6);
    z-index: 99;
    opacity: 0;
    transition: opacity 0.3s ease;
}

.sidebar-overlay.active {
    display: block;
    opacity: 1;
}

/* ---- Tablet & small desktop (≤ 900px) ---- */
@media (max-width: 900px) {
    #sidebar {
        transform: translateX(-100%);
        transition: transform 0.3s ease;
    }

    #sidebar.open {
        transform: translateX(0);
        box-shadow: 4px 0 20px rgba(0, 0, 0, 0.5);
    }

    .sidebar-toggle {
        display: block;
    }

    main {
        margin-left: 0;
        padding: 20px;
        padding-top: 60px;
    }

    .learning-stages {
        grid-template-columns: repeat(3, 1fr);
    }

    .memory-analysis {
        grid-template-columns: 1fr;
    }

    /* Prevent horizontal page overflow */
    .comparison-table {
        display: block;
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
    }

    .linked-list-viz {
        justify-content: flex-start;
        min-width: min-content;
    }

    .code-content {
        font-size: 12px;
    }
}

/* ---- Mobile (≤ 600px) ---- */
@media (max-width: 600px) {
    html {
        font-size: 15px;
    }

    main {
        padding: 14px;
        padding-top: 56px;
    }

    /* Welcome page */
    .welcome-title {
        font-size: 22px;
    }

    .welcome-subtitle {
        font-size: 13px;
        margin-bottom: 20px;
    }

    .overall-progress-card {
        padding: 16px;
        margin-bottom: 24px;
    }

    .section-title {
        font-size: 16px;
        margin-bottom: 14px;
    }

    .learning-stages {
        grid-template-columns: repeat(2, 1fr);
        gap: 8px;
    }

    .stage-card {
        padding: 14px 8px;
    }

    .stage-icon {
        font-size: 22px;
    }

    .stage-card h4 {
        font-size: 12px;
    }

    .quick-start-buttons {
        flex-direction: column;
    }

    /* Module view */
    .module-header {
        flex-wrap: wrap;
        gap: 10px;
    }

    #module-title {
        font-size: 18px;
    }

    .module-header-title span {
        font-size: 22px;
    }

    /* Tabs */
    .tabs {
        gap: 4px;
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
        flex-wrap: nowrap;
        padding-bottom: 4px;
    }

    .tab-btn {
        padding: 8px 12px;
        font-size: 12px;
        white-space: nowrap;
        flex-shrink: 0;
    }

    .tab-content, #module-content {
        padding: 14px;
        border-radius: var(--radius);
    }

    /* Concept sections */
    .concept-title {
        font-size: 18px;
    }

    .concept-text {
        font-size: 14px;
    }

    .concept-analogy {
        padding: 12px 14px;
    }

    /* Code blocks */
    .code-block {
        margin: 12px -14px;
        border-radius: 0;
        border-left: none;
        border-right: none;
    }

    .code-content {
        padding: 10px;
        font-size: 11px;
    }

    .line-number {
        min-width: 24px;
        padding-right: 8px;
        font-size: 10px;
    }

    /* Visualizer */
    .controls {
        flex-direction: column;
    }

    .controls input,
    .controls select {
        width: 100%;
    }

    .visualizer-container {
        padding: 14px;
        margin: 12px -14px;
        border-radius: 0;
    }

    .sorting-bars {
        height: 150px;
        padding: 12px;
    }

    .sorting-bar {
        min-width: 16px;
        font-size: 9px;
    }

    /* Linked list overflow */
    .linked-list-viz {
        padding: 12px 0;
    }

    .ll-node-content {
        width: 40px;
        height: 40px;
        font-size: 13px;
    }

    .ll-node-pointer {
        width: 20px;
        height: 40px;
    }

    /* Quiz */
    .quiz-question {
        padding: 14px;
    }

    .quiz-question h3 {
        font-size: 14px;
    }

    .quiz-option {
        padding: 12px;
        font-size: 13px;
    }

    .quiz-results .score-display {
        font-size: 36px;
    }

    /* Buttons */
    .btn {
        padding: 10px 16px;
        font-size: 13px;
    }

    .btn-large {
        padding: 12px 20px;
        font-size: 14px;
        width: 100%;
        justify-content: center;
    }

    /* Grid content */
    .tab-content-grid {
        grid-template-columns: 1fr;
    }

    /* Memory analysis */
    .memory-array {
        flex-wrap: wrap;
    }

    .memory-cell {
        padding: 8px 10px;
        min-width: 30px;
        font-size: 12px;
    }

    .step-controls {
        flex-wrap: wrap;
    }

    /* Fill-in-blank */
    .fill-blank-template {
        font-size: 12px;
        padding: 12px;
    }

    .blank-input {
        font-size: 12px;
        min-width: 50px;
    }

    /* Bug finder */
    .bug-code .code-line {
        padding: 2px 4px;
    }
}

/* ---- Very small screens (≤ 380px) ---- */
@media (max-width: 380px) {
    main {
        padding: 10px;
        padding-top: 52px;
    }

    .learning-stages {
        grid-template-columns: 1fr;
    }

    .welcome-title {
        font-size: 19px;
    }

    .tab-content, #module-content {
        padding: 10px;
    }

    #module-title {
        font-size: 16px;
    }
}