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

:root {
    --bg-primary: #001633;
    --bg-secondary: #0A2540;
    --bg-card: #0E2A47;
    --text-primary: #FFFFFF;
    --text-secondary: #78909C;
    --accent: #FFAB40;
    --accent-glow: rgba(255, 171, 64, 0.25);
    --accent2: #85D5E6;
    --accent2-glow: rgba(133, 213, 230, 0.2);
    --success: #0097A7;
    --success-glow: rgba(0, 151, 167, 0.3);
    --border: #1A3A5C;
}

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

/* ============ Header ============ */
header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    padding: 12px 24px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    backdrop-filter: blur(10px);
}

.header-left {
    display: flex;
    align-items: center;
    gap: 16px;
}

.back-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.85rem;
    transition: color 0.2s;
}

.back-link:hover {
    color: var(--accent);
}

.header-logo {
    width: 32px;
    height: 32px;
    object-fit: contain;
}

header h1 {
    font-size: 1.15rem;
    font-weight: 700;
    color: var(--text-primary);
}

.header-right {
    display: flex;
    align-items: center;
    gap: 20px;
}

/* ============ Nav Dots ============ */
.section-nav {
    display: flex;
    gap: 8px;
    align-items: center;
}

.nav-dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background: var(--border);
    transition: background 0.3s, transform 0.3s;
    cursor: pointer;
    border: none;
}

.nav-dot:hover {
    background: var(--text-secondary);
}

.nav-dot.active {
    background: var(--accent);
    transform: scale(1.4);
}

/* ============ Challenge Counter ============ */
.challenge-counter {
    display: flex;
    align-items: center;
    gap: 6px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 20px;
    padding: 6px 14px;
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--accent);
}

.counter-icon {
    font-size: 1rem;
}

/* ============ Course Sections ============ */
.course-section {
    min-height: 100vh;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 48px;
    align-items: center;
    padding: 80px 48px;
    max-width: 1300px;
    margin: 0 auto;
}

.course-section:nth-child(even):not(.hero-section):not(.conclusion-section) {
    direction: rtl;
}

.course-section:nth-child(even):not(.hero-section):not(.conclusion-section) > * {
    direction: ltr;
}

/* ============ Section Text ============ */
.section-text {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s ease, transform 0.6s ease;
}

.section-text.visible {
    opacity: 1;
    transform: translateY(0);
}

.section-text h2 {
    font-size: 1.8rem;
    font-weight: 800;
    margin-bottom: 20px;
    color: var(--text-primary);
    display: flex;
    align-items: baseline;
    gap: 12px;
}

.section-number {
    font-size: 3rem;
    font-weight: 900;
    color: var(--accent);
    opacity: 0.25;
    font-variant-numeric: tabular-nums;
    line-height: 1;
}

.section-text p {
    font-size: 0.95rem;
    color: var(--text-secondary);
    line-height: 1.65;
    margin-bottom: 14px;
}

.section-text strong {
    color: var(--text-primary);
}

.section-text em {
    color: var(--accent2);
    font-style: normal;
}

.section-text code {
    background: var(--bg-card);
    padding: 2px 8px;
    border-radius: 4px;
    font-size: 0.88rem;
    color: var(--accent2);
}

.concept-list {
    list-style: none;
    margin: 12px 0 16px;
    padding: 0;
}

.concept-list li {
    font-size: 0.92rem;
    color: var(--text-secondary);
    line-height: 1.6;
    padding: 4px 0 4px 20px;
    position: relative;
}

.concept-list li::before {
    content: '';
    position: absolute;
    left: 0;
    top: 12px;
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background: var(--accent);
    opacity: 0.5;
}

.concept-list li strong {
    color: var(--accent2);
}

/* ============ Section Visual ============ */
.section-visual {
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s ease 0.15s, transform 0.6s ease 0.15s;
}

.section-visual.visible {
    opacity: 1;
    transform: translateY(0);
}

.visual-container {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 16px;
    padding: 24px;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.visual-container svg,
.visual-container canvas {
    width: 100%;
    height: auto;
    display: block;
    border-radius: 8px;
}

/* ============ Hero Section ============ */
.hero-section {
    grid-template-columns: 1fr;
    text-align: center;
    position: relative;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 0;
}

#hero-canvas {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 0;
}

.hero-content {
    position: relative;
    z-index: 1;
    padding: 48px;
}

.hero-content h2 {
    font-size: 3.2rem;
    font-weight: 900;
    background: linear-gradient(135deg, var(--accent), #FFD180);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 16px;
}

.hero-subtitle {
    font-size: 1.25rem;
    color: var(--accent2);
    margin-bottom: 20px;
    font-weight: 500;
}

.hero-intro {
    font-size: 1rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto 32px;
    line-height: 1.65;
}

.scroll-hint {
    display: inline-block;
    padding: 12px 32px;
    background: var(--accent);
    color: var(--bg-primary);
    border-radius: 8px;
    font-size: 0.95rem;
    font-weight: 700;
    text-decoration: none;
    transition: filter 0.2s, box-shadow 0.2s, transform 0.2s;
    animation: bounce 2s infinite;
}

.scroll-hint:hover {
    filter: brightness(1.1);
    box-shadow: 0 0 20px var(--accent-glow);
}

@keyframes bounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-6px); }
}

/* ============ Neuron Comparison ============ */
.comparison-labels {
    display: flex;
    justify-content: center;
    gap: 24px;
    margin-bottom: 8px;
}

.comp-label {
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-secondary);
    transition: color 0.3s;
}

.comp-label.active {
    color: var(--accent);
}

.comparison-toggle {
    display: flex;
    justify-content: center;
    gap: 8px;
}

.toggle-btn {
    padding: 8px 20px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-secondary);
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 600;
    transition: all 0.2s;
}

.toggle-btn:hover {
    border-color: var(--accent);
    color: var(--text-primary);
}

.toggle-btn.active {
    background: var(--accent);
    color: var(--bg-primary);
    border-color: var(--accent);
}

/* ============ Slider Panel ============ */
.slider-panel {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.slider-group {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.slider-group-title {
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    color: var(--text-secondary);
    margin-bottom: 2px;
}

.slider-row {
    display: flex;
    align-items: center;
    gap: 12px;
}

.slider-row label {
    width: 28px;
    font-size: 0.85rem;
    color: var(--accent2);
    font-weight: 700;
    font-family: 'Courier New', monospace;
}

.slider-row input[type="range"] {
    flex: 1;
    accent-color: var(--accent);
    height: 4px;
}

.slider-row input[type="range"]:disabled {
    accent-color: var(--text-secondary);
    opacity: 0.5;
}

.value-display {
    width: 45px;
    text-align: right;
    font-variant-numeric: tabular-nums;
    font-size: 0.85rem;
    color: var(--text-primary);
    font-family: 'Courier New', monospace;
}

.output-row {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px;
    background: var(--bg-card);
    border-radius: 8px;
    border: 1px solid var(--border);
}

.output-label {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--text-secondary);
    font-family: 'Courier New', monospace;
}

.output-value {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--accent);
    font-variant-numeric: tabular-nums;
    font-family: 'Courier New', monospace;
    transition: color 0.2s;
}

/* ============ Formula Display ============ */
.formula-display {
    font-family: 'Courier New', monospace;
    font-size: 1rem;
    color: var(--accent2);
    text-align: center;
    padding: 12px 16px;
    background: var(--bg-card);
    border-radius: 8px;
    border: 1px solid var(--border);
}

/* ============ Function Selector ============ */
.func-selector {
    display: flex;
    gap: 8px;
    justify-content: center;
}

.func-btn {
    padding: 8px 20px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-primary);
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 600;
    transition: all 0.2s;
}

.func-btn:hover,
.data-btn:hover {
    border-color: var(--accent2);
}

.func-btn.active,
.data-btn.active {
    background: var(--accent2);
    color: var(--bg-primary);
    border-color: var(--accent2);
}

.data-btn {
    padding: 8px 20px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-primary);
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 600;
    transition: all 0.2s;
}

/* ============ Control Buttons ============ */
.ctrl-btn {
    padding: 8px 20px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-primary);
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 600;
    transition: all 0.2s;
}

.ctrl-btn:hover {
    border-color: var(--accent);
    color: var(--accent);
}

.ctrl-btn.secondary {
    color: var(--text-secondary);
}

.ctrl-btn.secondary:hover {
    color: var(--text-primary);
    border-color: var(--text-secondary);
}

.ctrl-btn.accent {
    background: var(--accent);
    color: var(--bg-primary);
    border-color: var(--accent);
}

.ctrl-btn.accent:hover {
    filter: brightness(1.1);
    box-shadow: 0 0 12px var(--accent-glow);
}

.classifier-controls,
.builder-controls,
.step-controls,
.gradient-btns {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
    justify-content: center;
}

.stat-display {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.stat-display strong {
    color: var(--accent);
    font-size: 1.1rem;
}

.network-info {
    text-align: center;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

/* ============ Step Text ============ */
.step-text {
    min-height: 48px;
    padding: 12px 16px;
    background: var(--bg-card);
    border-radius: 8px;
    border: 1px solid var(--border);
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.5;
    text-align: center;
}

.step-text strong {
    color: var(--accent);
}

.step-text .math {
    color: var(--accent2);
    font-family: 'Courier New', monospace;
}

/* ============ Gradient Controls ============ */
.gradient-controls {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.param-row {
    display: flex;
    align-items: center;
    gap: 12px;
}

.param-row label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    white-space: nowrap;
}

.param-row input[type="range"] {
    flex: 1;
    accent-color: var(--accent);
}

.gradient-stats {
    display: flex;
    justify-content: center;
    gap: 24px;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.gradient-stats strong {
    color: var(--accent);
}

/* ============ Challenge Box ============ */
.challenge-box {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 16px;
    transition: border-color 0.3s, box-shadow 0.3s;
}

.challenge-box.completed {
    border-color: var(--success);
    box-shadow: 0 0 16px var(--success-glow);
}

.challenge-header {
    display: flex;
    align-items: center;
    gap: 8px;
    margin-bottom: 8px;
}

.challenge-icon {
    color: var(--accent);
    font-size: 1rem;
}

.challenge-title {
    font-size: 0.85rem;
    font-weight: 700;
    color: var(--accent);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.challenge-status {
    margin-left: auto;
    font-size: 1.1rem;
}

.challenge-text {
    font-size: 0.88rem;
    color: var(--text-secondary);
    line-height: 1.5;
    margin-bottom: 10px;
}

.challenge-text strong {
    color: var(--text-primary);
}

/* ============ Challenge Progress ============ */
.challenge-progress {
    display: flex;
    align-items: center;
    gap: 12px;
}

.progress-bar {
    flex: 1;
    height: 6px;
    background: var(--bg-secondary);
    border-radius: 3px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: var(--accent);
    border-radius: 3px;
    transition: width 0.3s ease, background-color 0.3s;
    width: 0%;
}

.progress-fill.success {
    background: var(--success);
}

.progress-text {
    font-size: 0.8rem;
    color: var(--text-secondary);
    white-space: nowrap;
    font-variant-numeric: tabular-nums;
}

/* ============ Challenge Checklist ============ */
.challenge-checklist {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.check-item {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    transition: color 0.3s;
}

.check-item.done {
    color: var(--success);
}

.check-item .check-icon {
    font-size: 1rem;
    transition: color 0.3s;
}

.check-item.done .check-icon {
    color: var(--success);
}

/* ============ Quiz Container ============ */
.quiz-container {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.quiz-item {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 12px;
    transition: border-color 0.3s;
}

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

.quiz-item.wrong {
    border-color: #e85d4a;
}

.quiz-question {
    font-size: 0.85rem;
    color: var(--text-primary);
    margin-bottom: 8px;
}

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

.quiz-option {
    padding: 6px 14px;
    border: 1px solid var(--border);
    border-radius: 6px;
    background: var(--bg-card);
    color: var(--text-primary);
    cursor: pointer;
    font-size: 0.8rem;
    font-weight: 600;
    transition: all 0.2s;
}

.quiz-option:hover:not(.selected) {
    border-color: var(--accent2);
}

.quiz-option.selected.correct {
    background: var(--success);
    color: var(--bg-primary);
    border-color: var(--success);
}

.quiz-option.selected.wrong {
    background: #e85d4a;
    color: white;
    border-color: #e85d4a;
}

.quiz-option.disabled {
    pointer-events: none;
    opacity: 0.5;
}

.quiz-option.answer {
    border-color: var(--success);
    opacity: 1 !important;
}

/* ============ Calc Challenge ============ */
.calc-challenge-container {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.calc-step {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 8px 12px;
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 8px;
    font-size: 0.85rem;
}

.calc-step .calc-label {
    color: var(--accent2);
    font-family: 'Courier New', monospace;
    flex: 1;
}

.calc-step input {
    width: 70px;
    padding: 4px 8px;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 4px;
    color: var(--text-primary);
    font-size: 0.85rem;
    font-family: 'Courier New', monospace;
    text-align: center;
}

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

.calc-step .calc-result {
    width: 50px;
    text-align: center;
    font-weight: 700;
}

.calc-step .calc-result.correct {
    color: var(--success);
}

.calc-step .calc-result.wrong {
    color: #e85d4a;
}

.calc-step button {
    padding: 4px 12px;
    border: 1px solid var(--accent);
    border-radius: 4px;
    background: var(--accent);
    color: var(--bg-primary);
    cursor: pointer;
    font-size: 0.8rem;
    font-weight: 600;
}

/* ============ Conclusion ============ */
.conclusion-section {
    grid-template-columns: 1fr;
    text-align: center;
}

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

.conclusion-content h2 {
    font-size: 2.2rem;
    font-weight: 800;
    margin-bottom: 32px;
    background: linear-gradient(135deg, var(--accent), #FFD180);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.recap-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 16px;
    margin-bottom: 40px;
}

.recap-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 20px 16px;
    text-align: center;
}

.recap-num {
    display: block;
    font-size: 1.8rem;
    font-weight: 900;
    color: var(--accent);
    opacity: 0.3;
    margin-bottom: 4px;
}

.recap-card strong {
    display: block;
    font-size: 0.95rem;
    color: var(--text-primary);
    margin-bottom: 6px;
}

.recap-card p {
    font-size: 0.82rem;
    color: var(--text-secondary);
    line-height: 1.5;
}

.recap-card.done {
    border-color: var(--success);
    box-shadow: 0 0 12px var(--success-glow);
}

.recap-card.done .recap-num {
    color: var(--success);
    opacity: 0.8;
}

.recap-card.done strong {
    color: var(--success);
}

.final-score {
    display: inline-flex;
    align-items: center;
    gap: 10px;
    padding: 14px 28px;
    background: var(--bg-secondary);
    border: 2px solid var(--accent);
    border-radius: 12px;
    margin-bottom: 16px;
}

.score-icon {
    font-size: 1.5rem;
    color: var(--accent);
}

.score-text {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--accent);
}

.score-message {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 32px;
}

.next-steps {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 16px;
}

.cta-btn {
    display: inline-block;
    padding: 14px 36px;
    background: var(--accent);
    color: var(--bg-primary);
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 700;
    text-decoration: none;
    transition: filter 0.2s, box-shadow 0.2s;
}

.cta-btn:hover {
    filter: brightness(1.1);
    box-shadow: 0 0 20px var(--accent-glow);
}

.conclusion-section .back-link {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.9rem;
}

.conclusion-section .back-link:hover {
    color: var(--accent);
}

/* ============ Success Animation ============ */
@keyframes popIn {
    0% { transform: scale(0.5); opacity: 0; }
    60% { transform: scale(1.2); }
    100% { transform: scale(1); opacity: 1; }
}

.challenge-box.completed .challenge-status {
    animation: popIn 0.4s ease;
}

/* ============ Responsive ============ */
@media (max-width: 900px) {
    .course-section {
        grid-template-columns: 1fr;
        padding: 40px 20px;
        min-height: auto;
    }

    .course-section:nth-child(even):not(.hero-section):not(.conclusion-section) {
        direction: ltr;
    }

    .hero-content h2 {
        font-size: 2.2rem;
    }

    .section-text h2 {
        font-size: 1.4rem;
    }

    .section-number {
        font-size: 2rem;
    }

    header {
        flex-direction: column;
        gap: 10px;
    }

    .section-nav {
        display: none;
    }

    .slider-row label {
        width: 22px;
    }
}

/* ============ Mini Network Diagram (Section 4) ============ */
.mini-network-container {
    background: var(--bg-card, #0A2540);
    border: 1px solid rgba(133, 213, 230, 0.15);
    border-radius: 8px;
    padding: 8px;
    display: flex;
    justify-content: center;
    margin-bottom: 12px;
}

.mini-network-container svg {
    width: 100%;
    max-width: 280px;
    height: auto;
}

/* ============ MLP Demo Layout (Section 6) ============ */
.mlp-demo-layout {
    display: grid;
    grid-template-columns: 1fr auto;
    gap: 16px;
    align-items: start;
}

.mlp-canvas-area canvas {
    width: 100%;
    height: auto;
    display: block;
    border-radius: 8px;
}

.mlp-network-area svg {
    width: 200px;
    height: 300px;
    display: block;
}

@media (max-width: 900px) {
    .mlp-demo-layout {
        grid-template-columns: 1fr;
    }

    .mlp-network-area svg {
        width: 100%;
        max-width: 200px;
        margin: 0 auto;
    }
}