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

:root {
    --primary: #6c5ce7;
    --primary-dark: #5a4bd1;
    --primary-light: #a29bfe;
    --success: #00b894;
    --danger: #e74c3c;
    --warning: #fdcb6e;
    --info: #0984e3;
    --bg: #0f0f1a;
    --bg-card: #1a1a2e;
    --bg-code: #16213e;
    --bg-input: #0a0a15;
    --text: #e0e0e0;
    --text-dim: #8a8a9a;
    --text-bright: #ffffff;
    --border: #2a2a3e;
    --radius: 12px;
    --shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
    --glow: 0 0 20px rgba(108, 92, 231, 0.15);
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.7;
    min-height: 100vh;
}

a { color: var(--primary-light); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ========== SCROLLBAR ========== */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--primary); }

/* ========== LAYOUT ========== */
.course-header {
    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 50%, #0f3460 100%);
    border-bottom: 1px solid var(--border);
    padding: 20px 30px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(10px);
}

.course-header h1 {
    font-size: 20px;
    color: var(--text-bright);
    display: flex;
    align-items: center;
    gap: 10px;
}

.course-header .logo { font-size: 24px; }

.progress-bar-container {
    display: flex;
    align-items: center;
    gap: 10px;
    font-size: 13px;
    color: var(--text-dim);
}

.progress-bar {
    width: 200px;
    height: 8px;
    background: var(--border);
    border-radius: 4px;
    overflow: hidden;
}

.progress-bar-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary), var(--success));
    border-radius: 4px;
    transition: width 0.5s ease;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 40px 24px;
}

/* ========== TYPOGRAPHY ========== */
h1 { font-size: 36px; color: var(--text-bright); margin-bottom: 10px; }
h2 { font-size: 26px; color: var(--primary-light); margin: 40px 0 16px; border-left: 4px solid var(--primary); padding-left: 16px; }
h3 { font-size: 20px; color: var(--text-bright); margin: 30px 0 12px; }
h4 { font-size: 16px; color: var(--text); margin: 20px 0 8px; }
p { margin-bottom: 14px; }

.chapter-subtitle {
    font-size: 18px;
    color: var(--text-dim);
    margin-bottom: 30px;
}

/* ========== INTERACTIVE CODE EDITOR ========== */
.code-playground {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    margin: 20px 0;
    overflow: hidden;
    box-shadow: var(--shadow);
}

.code-playground-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 10px 16px;
    background: rgba(255, 255, 255, 0.03);
    border-bottom: 1px solid var(--border);
}

.code-playground-header .title {
    font-size: 13px;
    font-weight: 600;
    color: var(--text-dim);
    text-transform: uppercase;
    letter-spacing: 1px;
}

.code-playground-header .dots {
    display: flex;
    gap: 6px;
}

.code-playground-header .dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
}

.dot.red { background: #ff5f56; }
.dot.yellow { background: #ffbd2e; }
.dot.green { background: #27c93f; }

.code-editor {
    width: 100%;
    min-height: 120px;
    padding: 16px;
    background: var(--bg-code);
    color: #e0e0e0;
    border: none;
    font-family: 'Cascadia Code', 'Fira Code', 'Consolas', monospace;
    font-size: 14px;
    line-height: 1.6;
    resize: vertical;
    outline: none;
    tab-size: 4;
}

.code-editor:focus {
    box-shadow: inset 0 0 0 2px var(--primary);
}

.code-actions {
    display: flex;
    gap: 8px;
    padding: 10px 16px;
    background: rgba(255, 255, 255, 0.02);
    border-top: 1px solid var(--border);
}

.btn {
    padding: 8px 20px;
    border: none;
    border-radius: 6px;
    font-size: 13px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    display: inline-flex;
    align-items: center;
    gap: 6px;
}

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

.btn-run:hover { background: #00a884; transform: translateY(-1px); }

.btn-reset {
    background: transparent;
    color: var(--text-dim);
    border: 1px solid var(--border);
}

.btn-reset:hover { border-color: var(--text-dim); color: var(--text); }

.btn-copy {
    background: transparent;
    color: var(--text-dim);
    border: 1px solid var(--border);
    margin-left: auto;
}

.btn-copy:hover { border-color: var(--primary); color: var(--primary); }

.code-output {
    padding: 16px;
    background: var(--bg-input);
    border-top: 1px solid var(--border);
    font-family: 'Cascadia Code', 'Consolas', monospace;
    font-size: 13px;
    min-height: 50px;
    max-height: 300px;
    overflow-y: auto;
    white-space: pre-wrap;
    color: var(--success);
}

.code-output:empty::before {
    content: "Output will appear here after you click Run...";
    color: var(--text-dim);
    font-style: italic;
}

.code-output .error {
    color: var(--danger);
}

/* HTML/CSS Preview */
.preview-frame {
    width: 100%;
    min-height: 200px;
    background: white;
    border: none;
    border-top: 1px solid var(--border);
}

/* ========== CONCEPT BOXES ========== */
.concept-box {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    margin: 20px 0;
}

.analogy-box {
    background: linear-gradient(135deg, rgba(108, 92, 231, 0.1), rgba(162, 155, 254, 0.05));
    border: 1px solid rgba(108, 92, 231, 0.3);
    border-radius: var(--radius);
    padding: 20px 24px;
    margin: 20px 0;
}

.analogy-box::before {
    content: "💡 Think of it like...";
    display: block;
    font-weight: 700;
    color: var(--primary-light);
    margin-bottom: 8px;
    font-size: 14px;
}

.warning-box {
    background: rgba(231, 76, 60, 0.08);
    border: 1px solid rgba(231, 76, 60, 0.3);
    border-radius: var(--radius);
    padding: 20px 24px;
    margin: 20px 0;
}

.warning-box::before {
    content: "⚠️ Common Mistake";
    display: block;
    font-weight: 700;
    color: var(--danger);
    margin-bottom: 8px;
    font-size: 14px;
}

.tip-box {
    background: rgba(0, 184, 148, 0.08);
    border: 1px solid rgba(0, 184, 148, 0.3);
    border-radius: var(--radius);
    padding: 20px 24px;
    margin: 20px 0;
}

.tip-box::before {
    content: "✅ Pro Tip";
    display: block;
    font-weight: 700;
    color: var(--success);
    margin-bottom: 8px;
    font-size: 14px;
}

/* ========== QUIZ ========== */
.quiz-section {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 24px;
    margin: 30px 0;
}

.quiz-section h3 {
    margin-top: 0;
    color: var(--warning);
}

.quiz-question {
    margin: 20px 0;
    padding: 16px;
    background: rgba(255, 255, 255, 0.02);
    border-radius: 8px;
}

.quiz-question p {
    font-weight: 600;
    margin-bottom: 12px;
    color: var(--text-bright);
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.quiz-option {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 10px 16px;
    background: rgba(255, 255, 255, 0.03);
    border: 2px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
    font-size: 14px;
}

.quiz-option:hover {
    border-color: var(--primary);
    background: rgba(108, 92, 231, 0.1);
}

.quiz-option.selected {
    border-color: var(--primary);
    background: rgba(108, 92, 231, 0.15);
}

.quiz-option.correct {
    border-color: var(--success);
    background: rgba(0, 184, 148, 0.15);
}

.quiz-option.incorrect {
    border-color: var(--danger);
    background: rgba(231, 76, 60, 0.15);
}

.quiz-option input[type="radio"] { display: none; }

.quiz-feedback {
    margin-top: 12px;
    padding: 10px 16px;
    border-radius: 8px;
    font-size: 14px;
    display: none;
}

.quiz-feedback.show { display: block; }
.quiz-feedback.correct { background: rgba(0, 184, 148, 0.15); color: var(--success); }
.quiz-feedback.incorrect { background: rgba(231, 76, 60, 0.15); color: var(--danger); }

.btn-check {
    margin-top: 12px;
    background: var(--primary);
    color: white;
}

.btn-check:hover { background: var(--primary-dark); }

/* ========== INTERACTIVE EXERCISE (TRY IT) ========== */
.try-it {
    background: linear-gradient(135deg, rgba(0, 184, 148, 0.08), rgba(0, 184, 148, 0.02));
    border: 1px solid rgba(0, 184, 148, 0.3);
    border-radius: var(--radius);
    padding: 24px;
    margin: 30px 0;
}

.try-it h3 {
    color: var(--success);
    margin-top: 0;
    display: flex;
    align-items: center;
    gap: 8px;
}

.try-it .instructions {
    background: rgba(0, 0, 0, 0.2);
    padding: 16px;
    border-radius: 8px;
    margin: 12px 0;
    font-size: 14px;
}

.try-it .instructions ol {
    padding-left: 20px;
}

.try-it .instructions li {
    margin: 6px 0;
}

/* ========== COLLAPSIBLE SECTIONS ========== */
.collapsible {
    margin: 16px 0;
}

.collapsible-toggle {
    width: 100%;
    text-align: left;
    padding: 14px 20px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    color: var(--text-bright);
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: all 0.2s ease;
}

.collapsible-toggle:hover {
    border-color: var(--primary);
}

.collapsible-toggle .arrow {
    transition: transform 0.3s ease;
    font-size: 12px;
}

.collapsible-toggle.active .arrow {
    transform: rotate(90deg);
}

.collapsible-toggle.active {
    border-radius: var(--radius) var(--radius) 0 0;
    border-bottom: none;
}

.collapsible-content {
    display: none;
    padding: 20px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-top: none;
    border-radius: 0 0 var(--radius) var(--radius);
}

.collapsible-content.show { display: block; }

/* ========== STEP TRACKER ========== */
.step-tracker {
    display: flex;
    gap: 4px;
    margin: 30px 0;
    flex-wrap: wrap;
}

.step {
    flex: 1;
    min-width: 80px;
    text-align: center;
    padding: 10px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 8px;
    font-size: 12px;
    font-weight: 600;
    color: var(--text-dim);
    transition: all 0.3s ease;
}

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

.step.completed {
    background: rgba(0, 184, 148, 0.2);
    border-color: var(--success);
    color: var(--success);
}

/* ========== NAVIGATION ========== */
.chapter-nav {
    display: flex;
    justify-content: space-between;
    margin-top: 50px;
    padding-top: 30px;
    border-top: 1px solid var(--border);
}

.chapter-nav a {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 12px 24px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    color: var(--text);
    font-weight: 600;
    transition: all 0.2s ease;
}

.chapter-nav a:hover {
    border-color: var(--primary);
    color: var(--primary-light);
    text-decoration: none;
    transform: translateY(-2px);
}

/* ========== HOME PAGE ========== */
.hero {
    text-align: center;
    padding: 60px 20px;
}

.hero h1 {
    font-size: 42px;
    background: linear-gradient(135deg, var(--primary-light), var(--success));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 16px;
}

.hero p {
    font-size: 18px;
    color: var(--text-dim);
    max-width: 600px;
    margin: 0 auto 30px;
}

.chapter-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 16px;
    margin: 30px 0;
}

.chapter-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 20px;
    transition: all 0.3s ease;
    cursor: pointer;
    text-decoration: none;
    color: inherit;
    display: block;
}

.chapter-card:hover {
    border-color: var(--primary);
    transform: translateY(-4px);
    box-shadow: var(--glow);
    text-decoration: none;
}

.chapter-card .chapter-num {
    font-size: 12px;
    font-weight: 700;
    color: var(--primary);
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 8px;
}

.chapter-card h3 {
    font-size: 17px;
    color: var(--text-bright);
    margin: 0 0 8px;
}

.chapter-card p {
    font-size: 13px;
    color: var(--text-dim);
    margin: 0;
}

.chapter-card .status {
    margin-top: 12px;
    font-size: 12px;
    font-weight: 600;
}

.status-locked { color: var(--text-dim); }
.status-available { color: var(--primary-light); }
.status-completed { color: var(--success); }

.section-title {
    font-size: 14px;
    font-weight: 700;
    color: var(--text-dim);
    text-transform: uppercase;
    letter-spacing: 2px;
    margin: 40px 0 16px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border);
}

/* ========== INLINE CODE ========== */
code {
    background: rgba(108, 92, 231, 0.15);
    color: var(--primary-light);
    padding: 2px 8px;
    border-radius: 4px;
    font-family: 'Cascadia Code', 'Fira Code', 'Consolas', monospace;
    font-size: 0.9em;
}

/* ========== TABLE ========== */
table {
    width: 100%;
    border-collapse: collapse;
    margin: 16px 0;
    font-size: 14px;
}

th {
    background: rgba(108, 92, 231, 0.15);
    color: var(--primary-light);
    text-align: left;
    padding: 12px 16px;
    font-weight: 600;
}

td {
    padding: 10px 16px;
    border-bottom: 1px solid var(--border);
}

tr:hover td {
    background: rgba(255, 255, 255, 0.02);
}

/* ========== RESPONSIVE ========== */
@media (max-width: 768px) {
    .hero h1 { font-size: 28px; }
    .container { padding: 20px 16px; }
    .course-header { padding: 14px 16px; }
    .progress-bar { width: 120px; }
    .chapter-grid { grid-template-columns: 1fr; }
    .step-tracker { gap: 2px; }
    .step { min-width: 60px; font-size: 10px; padding: 6px; }
}