/* ===== ROOT VARIABLES ===== */
:root {
    --bg-primary: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --bg-card: rgba(22, 27, 34, 0.8);
    
    --text-primary: #f0f6fc;
    --text-secondary: #8b949e;
    --text-muted: #6e7681;
    
    --accent-blue: #0175C2;
    --accent-cyan: #00C4B3;
    --accent-purple: #a855f7;
    --accent-orange: #f97316;
    --accent-green: #22c55e;
    --accent-red: #ef4444;
    
    --gradient-primary: linear-gradient(135deg, var(--accent-blue), var(--accent-cyan));
    --gradient-card: linear-gradient(145deg, rgba(255,255,255,0.05), rgba(255,255,255,0.02));
    
    --border-color: rgba(48, 54, 61, 0.8);
    --shadow-lg: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    
    --font-main: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
    
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 20px;
    --radius-xl: 28px;
}

@media (max-width: 900px) {
    .objective-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 560px) {
    .objective-grid {
        grid-template-columns: 1fr;
    }
}

/* Learning objectives */
.learning-objectives {
    width: min(1100px, calc(100% - 32px));
    margin: 0 auto 2rem;
    padding: 1.5rem;
    border: 1px solid rgba(255, 255, 255, 0.14);
    border-radius: 20px;
    background: rgba(255, 255, 255, 0.06);
    backdrop-filter: blur(14px);
}

.learning-objectives h2 {
    margin: 0 0 1rem;
    color: #13b9fd;
    text-align: center;
}

.objective-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1rem;
}

.objective-grid article {
    padding: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: 14px;
    background: rgba(255, 255, 255, 0.045);
}

.objective-grid strong,
.objective-grid span {
    display: block;
}

.objective-grid strong {
    margin-bottom: 0.5rem;
}

.objective-grid span {
    color: rgba(255, 255, 255, 0.72);
    font-size: 0.9rem;
    line-height: 1.55;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-main);
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    overflow-x: hidden;
    line-height: 1.6;
}

/* ===== FLOATING ICONS BACKGROUND ===== */
.floating-icons {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 0;
    overflow: hidden;
}

.float-icon {
    position: absolute;
    opacity: 0.03;
    animation: float 20s ease-in-out infinite;
}

.icon-1 { width: 120px; top: 10%; left: 5%; animation-delay: 0s; }
.icon-2 { width: 80px; top: 60%; left: 15%; animation-delay: -4s; }
.icon-3 { width: 150px; top: 20%; right: 10%; animation-delay: -8s; }
.icon-4 { width: 60px; top: 70%; right: 20%; animation-delay: -12s; }
.icon-5 { width: 100px; bottom: 15%; left: 40%; animation-delay: -16s; }
.icon-6 { width: 90px; top: 40%; right: 5%; animation-delay: -6s; }

@keyframes float {
    0%, 100% { transform: translateY(0) rotate(0deg); }
    25% { transform: translateY(-20px) rotate(5deg); }
    50% { transform: translateY(0) rotate(0deg); }
    75% { transform: translateY(20px) rotate(-5deg); }
}

/* ===== LANDING PAGE ===== */
.landing-container {
    position: relative;
    z-index: 1;
    min-height: 100vh;
    padding: 40px 20px;
    display: flex;
    flex-direction: column;
    align-items: center;
}

/* Hero Section */
.hero {
    text-align: center;
    margin-bottom: 60px;
    animation: fadeInUp 0.8s ease-out;
}

.hero-icon {
    margin-bottom: 24px;
}

.dart-logo {
    width: 100px;
    height: auto;
    filter: drop-shadow(0 0 30px rgba(1, 117, 194, 0.5));
    animation: pulse 3s ease-in-out infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); filter: drop-shadow(0 0 30px rgba(1, 117, 194, 0.5)); }
    50% { transform: scale(1.05); filter: drop-shadow(0 0 50px rgba(1, 117, 194, 0.8)); }
}

.hero-title {
    font-size: clamp(2.5rem, 6vw, 4rem);
    font-weight: 800;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
    margin-bottom: 12px;
}

.hero-subtitle {
    font-size: clamp(1rem, 2.5vw, 1.4rem);
    color: var(--text-secondary);
    font-weight: 400;
}

.hero-line {
    width: 80px;
    height: 4px;
    background: var(--gradient-primary);
    border-radius: 2px;
    margin: 24px auto 0;
}

/* Topics Grid */
.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 24px;
    max-width: 1200px;
    width: 100%;
    padding: 0 20px;
}

/* Topic Cards */
.topic-card {
    background: var(--bg-card);
    backdrop-filter: blur(20px);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 28px;
    cursor: pointer;
    position: relative;
    overflow: hidden;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    animation: fadeInUp 0.6s ease-out backwards;
}

.topic-card:nth-child(1) { animation-delay: 0.1s; }
.topic-card:nth-child(2) { animation-delay: 0.15s; }
.topic-card:nth-child(3) { animation-delay: 0.2s; }
.topic-card:nth-child(4) { animation-delay: 0.25s; }
.topic-card:nth-child(5) { animation-delay: 0.3s; }
.topic-card:nth-child(6) { animation-delay: 0.35s; }
.topic-card:nth-child(7) { animation-delay: 0.4s; }
.topic-card:nth-child(8) { animation-delay: 0.45s; }
.topic-card:nth-child(9) { animation-delay: 0.5s; }

.topic-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: var(--gradient-primary);
    transform: scaleX(0);
    transition: transform 0.4s ease;
}

.topic-card:hover {
    transform: translateY(-8px);
    border-color: var(--accent-blue);
    box-shadow: 0 20px 40px rgba(1, 117, 194, 0.2);
}

.topic-card:hover::before {
    transform: scaleX(1);
}

.card-icon {
    font-size: 2.5rem;
    margin-bottom: 16px;
}

.topic-card h3 {
    font-size: 1.3rem;
    font-weight: 700;
    margin-bottom: 8px;
    color: var(--text-primary);
}

.topic-card p {
    font-size: 0.95rem;
    color: var(--text-secondary);
}

.card-arrow {
    position: absolute;
    right: 24px;
    top: 50%;
    transform: translateY(-50%);
    font-size: 1.5rem;
    color: var(--accent-blue);
    opacity: 0;
    transition: all 0.3s ease;
}

.topic-card:hover .card-arrow {
    opacity: 1;
    right: 20px;
}

/* Project Cards */
.project-card {
    background: linear-gradient(145deg, rgba(168, 85, 247, 0.1), rgba(1, 117, 194, 0.1));
    border-color: rgba(168, 85, 247, 0.3);
}

.project-card:hover {
    border-color: var(--accent-purple);
    box-shadow: 0 20px 40px rgba(168, 85, 247, 0.2);
}

.project-card::before {
    background: linear-gradient(90deg, var(--accent-purple), var(--accent-cyan));
}

/* Landing Footer */
.landing-footer {
    margin-top: 60px;
    text-align: center;
}

.landing-footer p {
    color: var(--text-muted);
    font-size: 0.9rem;
}

.landing-footer kbd {
    background: var(--bg-tertiary);
    padding: 4px 10px;
    border-radius: 6px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    border: 1px solid var(--border-color);
    margin: 0 2px;
}

/* ===== SLIDE CONTAINER ===== */
.slide-container {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--bg-primary);
    z-index: 100;
    display: flex;
    flex-direction: column;
    opacity: 1;
    transition: opacity 0.3s ease;
}

.slide-container.hidden {
    opacity: 0;
    pointer-events: none;
}

/* Slide Navigation */
.slide-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 24px;
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
}

.nav-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 20px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-family: var(--font-main);
    font-size: 0.95rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
}

.nav-btn:hover {
    background: var(--accent-blue);
    border-color: var(--accent-blue);
}

.slide-title {
    font-size: 1.3rem;
    font-weight: 700;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.slide-counter {
    font-family: var(--font-mono);
    font-size: 0.95rem;
    color: var(--text-secondary);
    background: var(--bg-tertiary);
    padding: 8px 16px;
    border-radius: var(--radius-sm);
}

/* Slide Content */
.slide-content {
    flex: 1;
    overflow-y: auto;
    padding: 40px;
    display: flex;
    flex-direction: column;
    align-items: center;
}

.slide {
    max-width: 900px;
    width: 100%;
    animation: slideIn 0.5s ease-out;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(30px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

.slide h2 {
    font-size: 2rem;
    font-weight: 700;
    margin-bottom: 24px;
    color: var(--text-primary);
    display: flex;
    align-items: center;
    gap: 16px;
}

.slide h2 .emoji {
    font-size: 2.5rem;
}

.slide h3 {
    font-size: 1.4rem;
    font-weight: 600;
    margin: 32px 0 16px;
    color: var(--accent-cyan);
}

.slide p {
    font-size: 1.1rem;
    line-height: 1.8;
    color: var(--text-secondary);
    margin-bottom: 16px;
}

.slide ul, .slide ol {
    margin: 16px 0;
    padding-left: 24px;
}

.slide li {
    font-size: 1.05rem;
    color: var(--text-secondary);
    margin-bottom: 10px;
    line-height: 1.7;
}

.slide li strong {
    color: var(--accent-cyan);
}

/* Code Blocks */
.code-block {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    margin: 20px 0;
    overflow: hidden;
}

.code-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 12px 16px;
    background: var(--bg-tertiary);
    border-bottom: 1px solid var(--border-color);
}

.code-lang {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--accent-cyan);
    text-transform: uppercase;
    font-weight: 600;
}

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

.code-dots span {
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.code-dots span:nth-child(1) { background: #ff5f57; }
.code-dots span:nth-child(2) { background: #ffbd2e; }
.code-dots span:nth-child(3) { background: #28c840; }

.code-body {
    padding: 20px;
    overflow-x: auto;
}

.code-body pre {
    margin: 0;
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.7;
    color: var(--text-primary);
}

/* Syntax Highlighting */
.keyword { color: #ff79c6; }
.string { color: #f1fa8c; }
.number { color: #bd93f9; }
.comment { color: #6272a4; font-style: italic; }
.function { color: #50fa7b; }
.type { color: #8be9fd; }
.operator { color: #ff79c6; }
.variable { color: #f8f8f2; }

/* Output Block */
.output-block {
    background: linear-gradient(135deg, rgba(34, 197, 94, 0.1), rgba(0, 196, 179, 0.1));
    border: 1px solid rgba(34, 197, 94, 0.3);
    border-radius: var(--radius-md);
    padding: 16px 20px;
    margin: 16px 0;
}

.output-label {
    font-family: var(--font-mono);
    font-size: 0.8rem;
    color: var(--accent-green);
    text-transform: uppercase;
    font-weight: 600;
    margin-bottom: 8px;
}

.output-text {
    font-family: var(--font-mono);
    font-size: 0.95rem;
    color: var(--text-primary);
    white-space: pre-wrap;
}

/* Info Boxes */
.info-box {
    border-radius: var(--radius-md);
    padding: 20px;
    margin: 20px 0;
}

.info-box.note {
    background: rgba(1, 117, 194, 0.1);
    border: 1px solid rgba(1, 117, 194, 0.3);
}

.info-box.warning {
    background: rgba(249, 115, 22, 0.1);
    border: 1px solid rgba(249, 115, 22, 0.3);
}

.info-box.tip {
    background: rgba(34, 197, 94, 0.1);
    border: 1px solid rgba(34, 197, 94, 0.3);
}

.info-box-title {
    font-weight: 700;
    margin-bottom: 8px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.info-box.note .info-box-title { color: var(--accent-blue); }
.info-box.warning .info-box-title { color: var(--accent-orange); }
.info-box.tip .info-box-title { color: var(--accent-green); }

/* Slide Controls */
.slide-controls {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 16px 24px;
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
}

.control-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 12px 24px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    color: var(--text-primary);
    font-family: var(--font-main);
    font-size: 0.95rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
}

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

.control-btn:disabled {
    opacity: 0.4;
    cursor: not-allowed;
}

.next-btn {
    background: var(--gradient-primary);
    border: none;
}

.next-btn:hover:not(:disabled) {
    transform: translateX(4px);
    box-shadow: 0 8px 20px rgba(1, 117, 194, 0.3);
}

/* Slide Indicators */
.slide-indicators {
    display: flex;
    gap: 8px;
}

.indicator {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background: var(--bg-tertiary);
    border: 2px solid var(--border-color);
    cursor: pointer;
    transition: all 0.3s ease;
}

.indicator:hover {
    border-color: var(--accent-blue);
}

.indicator.active {
    background: var(--accent-blue);
    border-color: var(--accent-blue);
    transform: scale(1.2);
}

/* Progress Bar */
.progress-bar {
    height: 4px;
    background: var(--bg-tertiary);
}

.progress-fill {
    height: 100%;
    background: var(--gradient-primary);
    transition: width 0.3s ease;
}

/* ===== ANIMATIONS ===== */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ===== SCROLLBAR ===== */
::-webkit-scrollbar {
    width: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
}

::-webkit-scrollbar-thumb {
    background: var(--bg-tertiary);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--accent-blue);
}

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
    .landing-container {
        padding: 24px 16px;
    }
    
    .hero {
        margin-bottom: 40px;
    }
    
    .dart-logo {
        width: 80px;
    }
    
    .topics-grid {
        grid-template-columns: 1fr;
        gap: 16px;
    }
    
    .topic-card {
        padding: 20px;
    }
    
    .slide-nav {
        padding: 12px 16px;
        flex-wrap: wrap;
        gap: 12px;
    }
    
    .slide-title {
        order: -1;
        width: 100%;
        text-align: center;
        font-size: 1.1rem;
    }
    
    .slide-content {
        padding: 24px 16px;
    }
    
    .slide h2 {
        font-size: 1.5rem;
    }
    
    .slide-controls {
        padding: 12px 16px;
    }
    
    .control-btn {
        padding: 10px 16px;
        font-size: 0.85rem;
    }
    
    .slide-indicators {
        display: none;
    }
}

@media (max-width: 900px) {
    .objective-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 560px) {
    .objective-grid {
        grid-template-columns: 1fr;
    }
}