/* AI Microlearning - Light Theme, Mobile-First */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&family=Space+Grotesk:wght@400;500;600;700&display=swap');

:root {
    --color-bg: #f8fafc;
    --color-bg-card: #ffffff;
    --color-bg-light: #f1f5f9;
    --color-bg-dark: #e2e8f0;
    --color-primary: #6366f1;
    --color-primary-light: #818cf8;
    --color-primary-dark: #4f46e5;
    --color-secondary: #0891b2;
    --color-accent: #f59e0b;
    --color-success: #10b981;
    --color-danger: #ef4444;
    --color-text: #1e293b;
    --color-text-muted: #64748b;
    --color-text-light: #94a3b8;
    --color-border: #e2e8f0;
    --gradient-primary: linear-gradient(135deg, #6366f1 0%, #8b5cf6 50%, #a855f7 100%);
    --gradient-secondary: linear-gradient(135deg, #0891b2 0%, #22d3ee 100%);
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.08);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.12);
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-tap-highlight-color: transparent;
}

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    line-height: 1.7;
    min-height: 100vh;
    -webkit-font-smoothing: antialiased;
}

/* ===== Mobile-First Layout ===== */
.lesson-container {
    width: 100%;
    max-width: 800px;
    margin: 0 auto;
    padding: 16px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===== Header ===== */
.lesson-header {
    text-align: center;
    padding: 24px 16px 32px;
}

.lesson-badge {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    background: var(--gradient-primary);
    color: white;
    padding: 6px 14px;
    border-radius: 50px;
    font-size: 0.7rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-bottom: 16px;
    box-shadow: var(--shadow-md);
}

.lesson-badge .icon {
    font-size: 0.9rem;
}

.lesson-title {
    font-family: 'Space Grotesk', sans-serif;
    font-size: 1.75rem;
    font-weight: 700;
    margin-bottom: 8px;
    color: var(--color-text);
    line-height: 1.2;
}

.lesson-subtitle {
    color: var(--color-text-muted);
    font-size: 1rem;
    max-width: 500px;
    margin: 0 auto;
}

/* ===== Progress Bar ===== */
.progress-wrapper {
    padding: 0 0 24px;
}

.progress-steps {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    position: relative;
}

.progress-steps::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 20px;
    right: 20px;
    height: 3px;
    background: var(--color-border);
    transform: translateY(-50%);
    z-index: 0;
}

.progress-step {
    width: 36px;
    height: 36px;
    border-radius: 50%;
    background: var(--color-bg-card);
    border: 3px solid var(--color-border);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: 0.85rem;
    color: var(--color-text-muted);
    transition: all 0.3s ease;
    cursor: pointer;
    position: relative;
    z-index: 1;
}

.progress-step.active {
    background: var(--gradient-primary);
    border-color: var(--color-primary);
    color: white;
    box-shadow: 0 0 0 4px rgba(99, 102, 241, 0.2);
}

.progress-step.completed {
    background: var(--color-success);
    border-color: var(--color-success);
    color: white;
}

.progress-step.completed::after {
    content: '✓';
    font-size: 0.9rem;
}

.progress-step.completed span {
    display: none;
}

.progress-label {
    text-align: center;
    font-size: 0.75rem;
    color: var(--color-text-muted);
    margin-top: 8px;
}

/* ===== Content Sections ===== */
.content-section {
    display: none;
    animation: fadeIn 0.4s ease;
}

.content-section.active {
    display: block;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(16px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ===== Cards ===== */
.content-card {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: 24px;
    margin-bottom: 20px;
    box-shadow: var(--shadow-sm);
}

.content-card h2 {
    font-family: 'Space Grotesk', sans-serif;
    font-size: 1.25rem;
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 10px;
    color: var(--color-text);
}

.content-card h2 .emoji {
    font-size: 1.5rem;
}

.content-card p {
    color: var(--color-text-muted);
    font-size: 1rem;
    margin-bottom: 12px;
}

.content-card p:last-child {
    margin-bottom: 0;
}

/* ===== Interactive Flip Cards ===== */
.interactive-cards {
    display: grid;
    grid-template-columns: 1fr;
    gap: 16px;
    margin: 20px 0;
}

.flip-card {
    height: 180px;
    perspective: 1000px;
    cursor: pointer;
}

.flip-card-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transition: transform 0.6s;
    transform-style: preserve-3d;
}

.flip-card.flipped .flip-card-inner {
    transform: rotateY(180deg);
}

.flip-card-front,
.flip-card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: var(--radius-lg);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 20px;
    text-align: center;
}

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

.flip-card-front .card-icon {
    font-size: 2.5rem;
    margin-bottom: 10px;
}

.flip-card-front h3 {
    font-size: 1rem;
    font-weight: 600;
}

.flip-card-front .tap-hint {
    position: absolute;
    bottom: 12px;
    font-size: 0.7rem;
    opacity: 0.8;
}

.flip-card-back {
    background: var(--color-bg-card);
    border: 2px solid var(--color-primary);
    transform: rotateY(180deg);
    font-size: 0.9rem;
    color: var(--color-text);
    line-height: 1.5;
}

/* ===== Timeline ===== */
.timeline {
    position: relative;
    padding-left: 32px;
    margin: 20px 0;
}

.timeline::before {
    content: '';
    position: absolute;
    left: 8px;
    top: 8px;
    bottom: 8px;
    width: 3px;
    background: var(--gradient-primary);
    border-radius: 3px;
}

.timeline-item {
    position: relative;
    padding-bottom: 24px;
    opacity: 0;
    transform: translateX(-16px);
    transition: all 0.4s ease;
}

.timeline-item.visible {
    opacity: 1;
    transform: translateX(0);
}

.timeline-item::before {
    content: '';
    position: absolute;
    left: -28px;
    top: 6px;
    width: 14px;
    height: 14px;
    background: white;
    border: 3px solid var(--color-primary);
    border-radius: 50%;
}

.timeline-year {
    font-family: 'Space Grotesk', sans-serif;
    font-weight: 700;
    color: var(--color-primary);
    font-size: 0.85rem;
    margin-bottom: 2px;
}

.timeline-title {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 4px;
    color: var(--color-text);
}

.timeline-desc {
    color: var(--color-text-muted);
    font-size: 0.9rem;
}

/* ===== Tabs ===== */
.tabs {
    margin: 20px 0;
}

.tab-buttons {
    display: flex;
    gap: 8px;
    margin-bottom: 16px;
    overflow-x: auto;
    padding-bottom: 4px;
    -webkit-overflow-scrolling: touch;
}

.tab-btn {
    padding: 10px 18px;
    background: var(--color-bg-light);
    border: none;
    border-radius: 50px;
    color: var(--color-text-muted);
    font-family: inherit;
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
    white-space: nowrap;
    flex-shrink: 0;
}

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

.tab-btn:hover:not(.active) {
    background: var(--color-bg-dark);
    color: var(--color-text);
}

.tab-content {
    display: none;
    padding: 20px;
    background: var(--color-bg-light);
    border-radius: var(--radius-md);
    animation: fadeIn 0.3s ease;
}

.tab-content.active {
    display: block;
}

/* ===== Quiz ===== */
.quiz-container {
    margin: 20px 0;
}

.quiz-question {
    background: var(--color-bg-light);
    border-radius: var(--radius-md);
    padding: 20px;
    margin-bottom: 16px;
}

.quiz-question h3 {
    font-size: 1rem;
    margin-bottom: 16px;
    display: flex;
    align-items: flex-start;
    gap: 10px;
    color: var(--color-text);
}

.quiz-question h3 .q-num {
    background: var(--gradient-primary);
    color: white;
    min-width: 26px;
    height: 26px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.8rem;
    flex-shrink: 0;
}

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

.quiz-option {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 14px 16px;
    background: var(--color-bg-card);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all 0.2s ease;
    -webkit-tap-highlight-color: transparent;
}

.quiz-option:hover,
.quiz-option:active {
    border-color: var(--color-primary-light);
    background: rgba(99, 102, 241, 0.05);
}

.quiz-option.selected {
    border-color: var(--color-primary);
    background: rgba(99, 102, 241, 0.1);
}

.quiz-option.correct {
    border-color: var(--color-success);
    background: rgba(16, 185, 129, 0.1);
}

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

.quiz-option .option-letter {
    min-width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--color-bg-light);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: 0.85rem;
    color: var(--color-text-muted);
}

.quiz-option.selected .option-letter {
    background: var(--color-primary);
    color: white;
}

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

.quiz-option.incorrect .option-letter {
    background: var(--color-danger);
    color: white;
}

.quiz-option .option-text {
    flex: 1;
    font-size: 0.95rem;
    color: var(--color-text);
}

/* ===== Comparison Table ===== */
.comparison-table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
    font-size: 0.9rem;
    background: var(--color-bg-card);
    border-radius: var(--radius-md);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
}

.comparison-table th,
.comparison-table td {
    padding: 12px 14px;
    text-align: left;
    border-bottom: 1px solid var(--color-border);
}

.comparison-table th {
    background: var(--color-bg-light);
    font-weight: 600;
    color: var(--color-primary-dark);
    font-size: 0.85rem;
}

.comparison-table tr:last-child td {
    border-bottom: none;
}

.comparison-table tr:hover td {
    background: rgba(99, 102, 241, 0.05);
}

/* ===== Info Boxes ===== */
.info-box {
    display: flex;
    gap: 14px;
    padding: 16px;
    border-radius: var(--radius-md);
    margin: 16px 0;
}

.info-box.tip {
    background: rgba(16, 185, 129, 0.1);
    border-left: 4px solid var(--color-success);
}

.info-box.warning {
    background: rgba(245, 158, 11, 0.1);
    border-left: 4px solid var(--color-accent);
}

.info-box.key {
    background: rgba(99, 102, 241, 0.1);
    border-left: 4px solid var(--color-primary);
}

.info-box .icon {
    font-size: 1.3rem;
    flex-shrink: 0;
}

.info-box .content {
    flex: 1;
    font-size: 0.95rem;
}

.info-box .content strong {
    display: block;
    margin-bottom: 4px;
    color: var(--color-text);
}

.info-box .content p {
    margin: 0;
    color: var(--color-text-muted);
}

/* ===== Image/Diagram Container ===== */
.diagram-container {
    background: var(--color-bg-light);
    border-radius: var(--radius-md);
    padding: 20px;
    margin: 16px 0;
    text-align: center;
}

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

.diagram-container .caption {
    margin-top: 12px;
    font-size: 0.85rem;
    color: var(--color-text-muted);
    font-style: italic;
}

/* ===== Feature List ===== */
.feature-list {
    list-style: none;
    margin: 16px 0;
}

.feature-list li {
    display: flex;
    align-items: flex-start;
    gap: 12px;
    padding: 12px 0;
    border-bottom: 1px solid var(--color-border);
}

.feature-list li:last-child {
    border-bottom: none;
}

.feature-list .check-icon {
    width: 22px;
    height: 22px;
    background: var(--color-success);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    flex-shrink: 0;
    margin-top: 2px;
}

.feature-list .feature-text {
    flex: 1;
    font-size: 0.95rem;
    color: var(--color-text);
}

/* ===== Navigation Buttons ===== */
.lesson-nav {
    display: flex;
    justify-content: space-between;
    gap: 12px;
    padding: 20px 0;
    margin-top: auto;
    border-top: 1px solid var(--color-border);
}

.nav-btn {
    padding: 14px 24px;
    font-family: inherit;
    font-size: 0.95rem;
    font-weight: 600;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 8px;
    -webkit-tap-highlight-color: transparent;
}

.nav-btn.prev {
    background: var(--color-bg-light);
    color: var(--color-text);
    border: 1px solid var(--color-border);
}

.nav-btn.prev:hover,
.nav-btn.prev:active {
    background: var(--color-bg-dark);
}

.nav-btn.next {
    background: var(--gradient-primary);
    color: white;
    box-shadow: var(--shadow-md);
    flex: 1;
    justify-content: center;
}

.nav-btn.next:hover,
.nav-btn.next:active {
    box-shadow: 0 6px 20px rgba(99, 102, 241, 0.35);
}

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

/* ===== Complete Button ===== */
.nav-btn.complete {
    background: linear-gradient(135deg, #10b981 0%, #059669 100%);
    color: white;
    flex: 1;
    justify-content: center;
    box-shadow: var(--shadow-md);
}

/* ===== Score Display ===== */
.score-display {
    text-align: center;
    padding: 24px;
    background: var(--color-bg-light);
    border-radius: var(--radius-lg);
    margin: 20px 0;
}

.score-display .score-number {
    font-family: 'Space Grotesk', sans-serif;
    font-size: 3rem;
    font-weight: 700;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.score-display .score-label {
    font-size: 1rem;
    color: var(--color-text-muted);
    margin-top: 4px;
}

/* ===== Tablet and Desktop ===== */
@media (min-width: 600px) {
    .lesson-container {
        padding: 24px;
    }

    .lesson-title {
        font-size: 2.25rem;
    }

    .interactive-cards {
        grid-template-columns: repeat(2, 1fr);
    }

    .flip-card {
        height: 200px;
    }

    .content-card {
        padding: 28px;
    }

    .lesson-nav {
        justify-content: space-between;
    }

    .nav-btn.next {
        flex: none;
        min-width: 180px;
    }
}

@media (min-width: 900px) {
    .interactive-cards {
        grid-template-columns: repeat(3, 1fr);
    }

    .lesson-title {
        font-size: 2.5rem;
    }
}

/* ===== Touch Device Optimizations ===== */
@media (hover: none) {
    .quiz-option:hover {
        border-color: var(--color-border);
        background: var(--color-bg-card);
    }

    .tab-btn:hover:not(.active) {
        background: var(--color-bg-light);
        color: var(--color-text-muted);
    }
}

/* ===== Safe Area for Mobile ===== */
@supports (padding-bottom: env(safe-area-inset-bottom)) {
    .lesson-nav {
        padding-bottom: calc(20px + env(safe-area-inset-bottom));
    }
}