/* ============================
   DESIGN TOKENS
   ============================ */
:root {
    /* Colors */
    --color-bg: #0a0a0f;
    --color-bg-card: #12121a;
    --color-bg-elevated: #1a1a26;
    --color-bg-hover: #22223a;
    --color-surface: #16161f;

    --color-primary: #6c5ce7;
    --color-primary-light: #a29bfe;
    --color-primary-dark: #4834d4;
    --color-primary-glow: rgba(108, 92, 231, 0.3);

    --color-accent: #00cec9;
    --color-accent-light: #55efc4;
    --color-accent-glow: rgba(0, 206, 201, 0.25);

    --color-success: #00b894;
    --color-warning: #fdcb6e;
    --color-error: #e17055;

    --color-text: #e8e8f0;
    --color-text-secondary: #9d9db5;
    --color-text-muted: #5f5f7a;
    --color-text-inverse: #0a0a0f;

    --color-border: rgba(255, 255, 255, 0.07);
    --color-border-active: rgba(108, 92, 231, 0.4);

    /* Gradients */
    --gradient-primary: linear-gradient(135deg, #6c5ce7 0%, #a29bfe 100%);
    --gradient-accent: linear-gradient(135deg, #00cec9 0%, #55efc4 100%);
    --gradient-dark: linear-gradient(180deg, #12121a 0%, #0a0a0f 100%);
    --gradient-card: linear-gradient(145deg, rgba(108, 92, 231, 0.08) 0%, rgba(0, 206, 201, 0.04) 100%);
    --gradient-hero: linear-gradient(135deg, rgba(108, 92, 231, 0.15) 0%, rgba(0, 206, 201, 0.1) 50%, rgba(108, 92, 231, 0.05) 100%);

    /* Typography */
    --font-main: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

    /* Spacing */
    --space-xs: 4px;
    --space-sm: 8px;
    --space-md: 16px;
    --space-lg: 24px;
    --space-xl: 32px;
    --space-2xl: 48px;
    --space-3xl: 64px;

    /* Borders */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    --radius-full: 9999px;

    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 24px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 8px 48px rgba(0, 0, 0, 0.4);
    --shadow-glow: 0 0 40px var(--color-primary-glow);

    /* Transitions */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 400ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-spring: 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275);

    /* Layout */
    --sidebar-width: 300px;
    --header-height: 60px;
}

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

html {
    scroll-behavior: smooth;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

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

/* ============================
   SPLASH SCREEN
   ============================ */
.splash-screen {
    position: fixed;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    background: var(--color-bg);
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.6s ease;
    overflow: hidden;
}

.splash-screen.active {
    opacity: 1;
    pointer-events: all;
}

.splash-bg-orbs {
    position: absolute;
    inset: 0;
    overflow: hidden;
}

.orb {
    position: absolute;
    border-radius: 50%;
    filter: blur(100px);
    opacity: 0.5;
    animation: orbFloat 8s ease-in-out infinite;
}

.orb-1 {
    width: 500px;
    height: 500px;
    background: var(--color-primary);
    top: -10%;
    right: -5%;
    animation-delay: 0s;
}

.orb-2 {
    width: 400px;
    height: 400px;
    background: var(--color-accent);
    bottom: -15%;
    left: -5%;
    animation-delay: -3s;
}

.orb-3 {
    width: 300px;
    height: 300px;
    background: var(--color-primary-dark);
    top: 40%;
    left: 30%;
    animation-delay: -5s;
}

@keyframes orbFloat {

    0%,
    100% {
        transform: translate(0, 0) scale(1);
    }

    33% {
        transform: translate(30px, -20px) scale(1.05);
    }

    66% {
        transform: translate(-20px, 20px) scale(0.95);
    }
}

.splash-content {
    position: relative;
    z-index: 1;
    text-align: center;
    padding: var(--space-xl);
    animation: fadeInUp 1s ease-out;
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }

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

.splash-badge {
    display: inline-block;
    padding: 6px 18px;
    background: rgba(108, 92, 231, 0.15);
    border: 1px solid rgba(108, 92, 231, 0.3);
    border-radius: var(--radius-full);
    color: var(--color-primary-light);
    font-size: 0.85rem;
    font-weight: 500;
    margin-bottom: var(--space-xl);
    letter-spacing: 0.5px;
}

.splash-title {
    font-size: clamp(2.5rem, 7vw, 5rem);
    font-weight: 900;
    line-height: 1.1;
    margin-bottom: var(--space-lg);
}

.title-line {
    display: block;
}

.title-line.accent {
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.splash-subtitle {
    font-size: 1.15rem;
    color: var(--color-text-secondary);
    max-width: 540px;
    margin: 0 auto var(--space-2xl);
    line-height: 1.7;
}

.splash-stats {
    display: flex;
    justify-content: center;
    gap: var(--space-2xl);
    margin-bottom: var(--space-2xl);
}

.stat-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--space-xs);
}

.stat-number {
    font-size: 2rem;
    font-weight: 800;
    background: var(--gradient-accent);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 1px;
    font-weight: 500;
}

/* ============================
   BUTTONS
   ============================ */
.btn-primary {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 14px 36px;
    background: var(--gradient-primary);
    color: white;
    border: none;
    border-radius: var(--radius-full);
    font-family: var(--font-main);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-base);
    position: relative;
    overflow: hidden;
}

.btn-primary::before {
    content: '';
    position: absolute;
    inset: 0;
    background: linear-gradient(135deg, rgba(255, 255, 255, 0.2) 0%, rgba(255, 255, 255, 0) 100%);
    opacity: 0;
    transition: opacity var(--transition-fast);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow), var(--shadow-md);
}

.btn-primary:hover::before {
    opacity: 1;
}

.btn-primary:active {
    transform: translateY(0);
}

.btn-large {
    padding: 18px 48px;
    font-size: 1.1rem;
}

.btn-secondary {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 12px 28px;
    background: transparent;
    color: var(--color-text);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-full);
    font-family: var(--font-main);
    font-size: 0.95rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-base);
}

.btn-secondary:hover {
    background: var(--color-bg-hover);
    border-color: var(--color-border-active);
    transform: translateY(-1px);
}

.btn-nav {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 12px 24px;
    background: var(--color-bg-elevated);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    color: var(--color-text);
    font-family: var(--font-main);
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-base);
}

.btn-nav:hover {
    background: var(--color-bg-hover);
    border-color: var(--color-border-active);
    transform: translateY(-1px);
}

.btn-nav.primary {
    background: var(--gradient-primary);
    border-color: transparent;
    color: white;
}

.btn-nav.primary:hover {
    box-shadow: var(--shadow-glow);
}

/* ============================
   COURSE APP LAYOUT
   ============================ */
.course-app {
    display: none;
    min-height: 100vh;
}

.course-app.active {
    display: flex;
}

/* ============================
   SIDEBAR
   ============================ */
.sidebar {
    position: fixed;
    left: 0;
    top: 0;
    bottom: 0;
    width: var(--sidebar-width);
    background: var(--color-surface);
    border-right: 1px solid var(--color-border);
    display: flex;
    flex-direction: column;
    z-index: 100;
    transition: transform var(--transition-base);
    overflow-y: auto;
}

.sidebar-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--space-lg);
    border-bottom: 1px solid var(--color-border);
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.logo-icon {
    width: 36px;
    height: 36px;
    background: var(--gradient-primary);
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 800;
    font-size: 1.1rem;
    color: white;
}

.logo-text {
    font-weight: 700;
    font-size: 1rem;
    color: var(--color-text);
}

.sidebar-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--color-text-secondary);
    cursor: pointer;
    padding: var(--space-xs);
    border-radius: var(--radius-sm);
    transition: all var(--transition-fast);
}

.sidebar-toggle:hover {
    color: var(--color-text);
    background: var(--color-bg-hover);
}

/* Progress Bar */
.progress-bar-container {
    padding: var(--space-md) var(--space-lg);
    border-bottom: 1px solid var(--color-border);
}

.progress-bar {
    height: 6px;
    background: var(--color-bg-hover);
    border-radius: var(--radius-full);
    overflow: hidden;
    margin-bottom: var(--space-sm);
}

.progress-fill {
    height: 100%;
    background: var(--gradient-accent);
    border-radius: var(--radius-full);
    transition: width var(--transition-slow);
    position: relative;
}

.progress-fill::after {
    content: '';
    position: absolute;
    right: 0;
    top: 0;
    bottom: 0;
    width: 20px;
    background: rgba(255, 255, 255, 0.3);
    filter: blur(4px);
}

.progress-text {
    font-size: 0.8rem;
    color: var(--color-text-muted);
    font-weight: 500;
}

/* Sidebar Reset Button */
.sidebar-footer {
    padding: var(--space-md) var(--space-lg);
    border-top: 1px solid var(--color-border);
}

.btn-reset {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    width: 100%;
    padding: 10px var(--space-md);
    background: transparent;
    border: 1px solid rgba(225, 112, 85, 0.25);
    border-radius: var(--radius-sm);
    color: var(--color-error);
    font-family: var(--font-main);
    font-size: 0.82rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.btn-reset:hover {
    background: rgba(225, 112, 85, 0.1);
    border-color: rgba(225, 112, 85, 0.4);
}

.btn-reset svg {
    width: 14px;
    height: 14px;
}

/* Reset Confirm Modal */
.reset-modal-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(8px);
    z-index: 200;
    align-items: center;
    justify-content: center;
}

.reset-modal-overlay.visible {
    display: flex;
}

.reset-modal {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    max-width: 400px;
    width: 90%;
    text-align: center;
    animation: feedbackSlide 0.3s ease;
}

.reset-modal h3 {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--space-sm);
}

.reset-modal p {
    font-size: 0.9rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--space-lg);
    line-height: 1.6;
}

.reset-modal-btns {
    display: flex;
    gap: var(--space-sm);
    justify-content: center;
}

.reset-modal-btns button {
    padding: 10px 24px;
    border-radius: var(--radius-full);
    font-family: var(--font-main);
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    border: none;
    transition: all var(--transition-fast);
}

.btn-cancel {
    background: var(--color-bg-elevated);
    color: var(--color-text);
    border: 1px solid var(--color-border) !important;
}

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

.btn-confirm-reset {
    background: var(--color-error);
    color: white;
}

.btn-confirm-reset:hover {
    opacity: 0.9;
    transform: translateY(-1px);
}

/* Sidebar Modules */
.sidebar-modules {
    padding: var(--space-md) var(--space-sm);
    flex: 1;
    overflow-y: auto;
}

.sidebar-module {
    margin-bottom: var(--space-xs);
}

.module-header {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 10px var(--space-md);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--color-text-secondary);
    user-select: none;
}

.module-header:hover {
    background: var(--color-bg-hover);
    color: var(--color-text);
}

.module-header.active {
    color: var(--color-primary-light);
}

.module-header .module-icon {
    font-size: 1rem;
    width: 24px;
    text-align: center;
    flex-shrink: 0;
}

.module-header .module-chevron {
    margin-left: auto;
    transition: transform var(--transition-fast);
    font-size: 0.7rem;
    color: var(--color-text-muted);
}

.module-header.expanded .module-chevron {
    transform: rotate(90deg);
}

.module-lessons {
    display: none;
    padding-left: calc(var(--space-md) + 24px + var(--space-sm));
}

.module-lessons.expanded {
    display: block;
}

.lesson-item {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 8px var(--space-md);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-size: 0.82rem;
    color: var(--color-text-muted);
    position: relative;
}

.lesson-item::before {
    content: '';
    position: absolute;
    left: -12px;
    top: 0;
    bottom: 0;
    width: 2px;
    background: var(--color-border);
}

.lesson-item:last-child::before {
    bottom: 50%;
}

.lesson-item:hover {
    background: var(--color-bg-hover);
    color: var(--color-text);
}

.lesson-item.active {
    background: rgba(108, 92, 231, 0.1);
    color: var(--color-primary-light);
}

.lesson-item.completed {
    color: var(--color-success);
}

.lesson-check {
    width: 16px;
    height: 16px;
    border-radius: 50%;
    border: 2px solid var(--color-text-muted);
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.6rem;
    transition: all var(--transition-fast);
}

.lesson-item.active .lesson-check {
    border-color: var(--color-primary-light);
    background: rgba(108, 92, 231, 0.2);
}

.lesson-item.completed .lesson-check {
    border-color: var(--color-success);
    background: var(--color-success);
    color: white;
}

/* ============================
   MOBILE HEADER
   ============================ */
.mobile-header {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: var(--header-height);
    background: rgba(10, 10, 15, 0.9);
    backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--color-border);
    z-index: 90;
    align-items: center;
    padding: 0 var(--space-md);
    gap: var(--space-md);
}

.hamburger {
    background: none;
    border: none;
    color: var(--color-text);
    cursor: pointer;
    padding: var(--space-xs);
}

.logo-small {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-weight: 600;
    font-size: 0.9rem;
}

.logo-icon-small {
    width: 28px;
    height: 28px;
    background: var(--gradient-primary);
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 800;
    font-size: 0.85rem;
    color: white;
}

.mobile-progress {
    margin-left: auto;
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--color-accent);
}

.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.6);
    backdrop-filter: blur(4px);
    z-index: 95;
}

/* ============================
   MAIN CONTENT
   ============================ */
.main-content {
    margin-left: var(--sidebar-width);
    flex: 1;
    min-height: 100vh;
    padding: var(--space-3xl) var(--space-2xl);
    animation: contentFade 0.4s ease;
}

.main-content>.fade-in {
    max-width: 760px;
    margin: 0 auto;
}

@keyframes contentFade {
    from {
        opacity: 0;
        transform: translateY(10px);
    }

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

/* Lesson Content Styling */
.lesson-header {
    margin-bottom: var(--space-2xl);
}

.lesson-module-label {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 6px 14px;
    background: rgba(108, 92, 231, 0.1);
    border: 1px solid rgba(108, 92, 231, 0.2);
    border-radius: var(--radius-full);
    color: var(--color-primary-light);
    font-size: 0.8rem;
    font-weight: 500;
    margin-bottom: var(--space-md);
}

.lesson-title {
    font-size: clamp(1.8rem, 4vw, 2.5rem);
    font-weight: 800;
    line-height: 1.2;
    margin-bottom: var(--space-md);
    background: linear-gradient(135deg, var(--color-text) 0%, var(--color-text-secondary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.lesson-description {
    font-size: 1.1rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
}

/* Content Blocks */
.content-block {
    margin-bottom: var(--space-xl);
}

.content-block h2 {
    font-size: 1.4rem;
    font-weight: 700;
    margin-bottom: var(--space-md);
    color: var(--color-text);
}

.content-block h3 {
    font-size: 1.15rem;
    font-weight: 600;
    margin-bottom: var(--space-md);
    color: var(--color-text);
}

.content-block p {
    font-size: 1rem;
    line-height: 1.8;
    color: var(--color-text-secondary);
    margin-bottom: var(--space-md);
}

.content-block ul,
.content-block ol {
    padding-left: var(--space-lg);
    margin-bottom: var(--space-md);
}

.content-block li {
    font-size: 1rem;
    line-height: 1.8;
    color: var(--color-text-secondary);
    margin-bottom: var(--space-sm);
}

/* Info Box */
.info-box {
    padding: var(--space-lg);
    border-radius: var(--radius-md);
    margin-bottom: var(--space-xl);
    border: 1px solid;
}

.info-box.tip {
    background: rgba(0, 206, 201, 0.05);
    border-color: rgba(0, 206, 201, 0.2);
}

.info-box.tip .info-box-title {
    color: var(--color-accent);
}

.info-box.warning {
    background: rgba(253, 203, 110, 0.05);
    border-color: rgba(253, 203, 110, 0.2);
}

.info-box.warning .info-box-title {
    color: var(--color-warning);
}

.info-box.important {
    background: rgba(108, 92, 231, 0.05);
    border-color: rgba(108, 92, 231, 0.2);
}

.info-box.important .info-box-title {
    color: var(--color-primary-light);
}

.info-box-title {
    font-weight: 700;
    font-size: 0.9rem;
    margin-bottom: var(--space-sm);
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.info-box p {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
    margin: 0;
}

/* Code Blocks */
.code-block {
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-lg);
    margin-bottom: var(--space-xl);
    overflow-x: auto;
    position: relative;
}

.code-block-label {
    position: absolute;
    top: 0;
    right: 0;
    padding: 4px 12px;
    background: var(--color-bg-elevated);
    border-radius: 0 var(--radius-md) 0 var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.7rem;
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 1px;
}

.code-block pre {
    font-family: var(--font-mono);
    font-size: 0.88rem;
    line-height: 1.7;
    color: var(--color-text);
    white-space: pre-wrap;
}

.code-block .highlight {
    color: var(--color-accent);
}

.code-block .comment {
    color: var(--color-text-muted);
}

/* Example Comparison */
.example-comparison {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-md);
    margin-bottom: var(--space-xl);
}

.example-card {
    padding: var(--space-lg);
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border);
}

.example-card.bad {
    background: rgba(225, 112, 85, 0.05);
    border-color: rgba(225, 112, 85, 0.2);
}

.example-card.good {
    background: rgba(0, 184, 148, 0.05);
    border-color: rgba(0, 184, 148, 0.2);
}

.example-card-label {
    font-size: 0.8rem;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: var(--space-sm);
}

.example-card.bad .example-card-label {
    color: var(--color-error);
}

.example-card.good .example-card-label {
    color: var(--color-success);
}

.example-card p {
    font-size: 0.9rem;
    line-height: 1.6;
    color: var(--color-text-secondary);
    margin: 0;
}

/* Feature Cards Grid */
.feature-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: var(--space-md);
    margin-bottom: var(--space-xl);
}

.feature-card {
    padding: var(--space-lg);
    background: var(--gradient-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
}

.feature-card:hover {
    border-color: var(--color-border-active);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.feature-card-icon {
    font-size: 1.5rem;
    margin-bottom: var(--space-md);
}

.feature-card h4 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: var(--space-sm);
    color: var(--color-text);
}

.feature-card p {
    font-size: 0.88rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
    margin: 0;
}

/* Steps (numbered list with visual style) */
.steps-list {
    list-style: none;
    padding: 0;
    counter-reset: step-counter;
    margin-bottom: var(--space-xl);
}

.step-item {
    display: flex;
    gap: var(--space-md);
    padding: var(--space-lg) 0;
    border-bottom: 1px solid var(--color-border);
    counter-increment: step-counter;
}

.step-item:last-child {
    border-bottom: none;
}

.step-number {
    width: 40px;
    height: 40px;
    background: var(--gradient-primary);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 0.9rem;
    color: white;
    flex-shrink: 0;
}

.step-content h4 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: var(--space-xs);
    color: var(--color-text);
}

.step-content p {
    font-size: 0.92rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
    margin: 0;
}

/* ============================
   QUIZ STYLES
   ============================ */
.quiz-container {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-xl);
}

.quiz-header {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    margin-bottom: var(--space-xl);
}

.quiz-icon {
    width: 48px;
    height: 48px;
    background: var(--gradient-primary);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.4rem;
}

.quiz-header-text h3 {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 2px;
}

.quiz-header-text p {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    margin: 0;
}

.quiz-question {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: var(--space-lg);
    line-height: 1.6;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
    margin-bottom: var(--space-lg);
}

.quiz-option {
    display: flex;
    align-items: flex-start;
    gap: var(--space-md);
    padding: var(--space-md) var(--space-lg);
    background: var(--color-bg-elevated);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.5;
}

.quiz-option:hover {
    border-color: var(--color-border-active);
    background: var(--color-bg-hover);
    color: var(--color-text);
}

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

.quiz-option.correct {
    border-color: var(--color-success);
    background: rgba(0, 184, 148, 0.1);
    color: var(--color-success);
}

.quiz-option.incorrect {
    border-color: var(--color-error);
    background: rgba(225, 112, 85, 0.1);
    color: var(--color-error);
}

.quiz-option-letter {
    width: 28px;
    height: 28px;
    border-radius: 50%;
    border: 2px solid var(--color-text-muted);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
    font-size: 0.8rem;
    flex-shrink: 0;
    transition: all var(--transition-fast);
}

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

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

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

.quiz-feedback {
    padding: var(--space-md) var(--space-lg);
    border-radius: var(--radius-md);
    font-size: 0.95rem;
    line-height: 1.6;
    display: none;
    margin-bottom: var(--space-md);
    animation: feedbackSlide 0.3s ease;
}

@keyframes feedbackSlide {
    from {
        opacity: 0;
        transform: translateY(-8px);
    }

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

.quiz-feedback.correct {
    display: block;
    background: rgba(0, 184, 148, 0.1);
    border: 1px solid rgba(0, 184, 148, 0.3);
    color: var(--color-success);
}

.quiz-feedback.incorrect {
    display: block;
    background: rgba(225, 112, 85, 0.1);
    border: 1px solid rgba(225, 112, 85, 0.3);
    color: var(--color-error);
}

.quiz-check-btn {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 12px 28px;
    background: var(--gradient-primary);
    color: white;
    border: none;
    border-radius: var(--radius-full);
    font-family: var(--font-main);
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-base);
}

.quiz-check-btn:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-glow);
}

.quiz-check-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
}

/* Interactive Exercises */
.exercise-container {
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-xl);
}

.exercise-header {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    margin-bottom: var(--space-lg);
}

.exercise-icon {
    width: 48px;
    height: 48px;
    background: var(--gradient-accent);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.4rem;
}

.exercise-header-text h3 {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: 2px;
}

.exercise-header-text p {
    font-size: 0.85rem;
    color: var(--color-text-muted);
    margin: 0;
}

.exercise-textarea {
    width: 100%;
    min-height: 120px;
    background: var(--color-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: var(--space-md);
    color: var(--color-text);
    font-family: var(--font-mono);
    font-size: 0.9rem;
    line-height: 1.6;
    resize: vertical;
    transition: border-color var(--transition-fast);
    margin-bottom: var(--space-md);
}

.exercise-textarea:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(108, 92, 231, 0.1);
}

.exercise-textarea::placeholder {
    color: var(--color-text-muted);
}

.exercise-hint {
    padding: var(--space-md);
    background: rgba(108, 92, 231, 0.05);
    border-radius: var(--radius-sm);
    margin-bottom: var(--space-md);
    display: none;
}

.exercise-hint.visible {
    display: block;
    animation: feedbackSlide 0.3s ease;
}

.exercise-hint p {
    font-size: 0.9rem;
    color: var(--color-primary-light);
    line-height: 1.6;
    margin: 0;
}

/* ============================
   NAVIGATION FOOTER
   ============================ */
.lesson-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: var(--space-xl);
    margin-top: var(--space-2xl);
    border-top: 1px solid var(--color-border);
}

.lesson-nav .spacer {
    flex: 1;
}

/* ============================
   COMPLETION CARD
   ============================ */
.completion-card {
    text-align: center;
    padding: var(--space-3xl) var(--space-xl);
    background: var(--gradient-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-xl);
    margin-bottom: var(--space-xl);
}

.completion-icon {
    font-size: 4rem;
    margin-bottom: var(--space-lg);
    animation: bounce 1s ease infinite;
}

@keyframes bounce {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-10px);
    }
}

.completion-card h2 {
    font-size: 1.8rem;
    font-weight: 800;
    margin-bottom: var(--space-md);
    background: var(--gradient-accent);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.completion-card p {
    font-size: 1.05rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
    max-width: 500px;
    margin: 0 auto;
}

/* Community CTA Card */
.community-cta {
    background: var(--gradient-hero);
    border: 1px solid rgba(108, 92, 231, 0.25);
    border-radius: var(--radius-xl);
    padding: var(--space-2xl);
    text-align: center;
    margin-top: var(--space-xl);
    margin-bottom: var(--space-xl);
}

.community-cta-icon {
    font-size: 2.5rem;
    margin-bottom: var(--space-md);
}

.community-cta h3 {
    font-size: 1.3rem;
    font-weight: 700;
    color: var(--color-text);
    margin-bottom: var(--space-sm);
}

.community-cta p {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
    max-width: 480px;
    margin: 0 auto var(--space-lg);
}

.community-cta .btn-community {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: 14px 32px;
    background: var(--gradient-accent);
    color: var(--color-text-inverse);
    border: none;
    border-radius: var(--radius-full);
    font-family: var(--font-main);
    font-size: 0.95rem;
    font-weight: 700;
    cursor: pointer;
    text-decoration: none;
    transition: all var(--transition-base);
}

.community-cta .btn-community:hover {
    transform: translateY(-2px);
    box-shadow: 0 0 30px var(--color-accent-glow), var(--shadow-md);
}

/* Footer */
.site-footer {
    border-top: 1px solid var(--color-border);
    padding: var(--space-xl) var(--space-2xl);
    margin-top: var(--space-2xl);
    text-align: center;
}

.site-footer p {
    font-size: 0.82rem;
    color: var(--color-text-muted);
    margin: 0;
}

.site-footer a {
    color: var(--color-primary-light);
    text-decoration: none;
    transition: color var(--transition-fast);
}

.site-footer a:hover {
    color: var(--color-accent);
}

/* Checklist */
.checklist {
    list-style: none;
    padding: 0;
    margin-bottom: var(--space-xl);
}

.checklist-item {
    display: flex;
    align-items: flex-start;
    gap: var(--space-md);
    padding: var(--space-md) var(--space-lg);
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    margin-bottom: var(--space-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.checklist-item:hover {
    border-color: var(--color-border-active);
}

.checklist-item.checked {
    border-color: rgba(0, 184, 148, 0.3);
    background: rgba(0, 184, 148, 0.05);
}

.checklist-checkbox {
    width: 22px;
    height: 22px;
    border-radius: 6px;
    border: 2px solid var(--color-text-muted);
    flex-shrink: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.8rem;
    transition: all var(--transition-fast);
    margin-top: 2px;
}

.checklist-item.checked .checklist-checkbox {
    background: var(--color-success);
    border-color: var(--color-success);
    color: white;
}

.checklist-text {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.5;
}

.checklist-item.checked .checklist-text {
    color: var(--color-success);
    text-decoration: line-through;
    text-decoration-color: rgba(0, 184, 148, 0.3);
}

/* ============================
   RESPONSIVE
   ============================ */
@media (max-width: 900px) {
    .sidebar {
        transform: translateX(-100%);
    }

    .sidebar.open {
        transform: translateX(0);
    }

    .sidebar-toggle {
        display: block;
    }

    .sidebar-overlay.visible {
        display: block;
    }

    .mobile-header {
        display: flex;
    }

    .main-content {
        margin-left: 0;
        padding: calc(var(--header-height) + var(--space-xl)) var(--space-md) var(--space-xl);
    }

    .example-comparison {
        grid-template-columns: 1fr;
    }

    .splash-stats {
        gap: var(--space-lg);
    }

    .stat-number {
        font-size: 1.5rem;
    }
}

@media (max-width: 500px) {
    .splash-title {
        font-size: 2rem;
    }

    .splash-subtitle {
        font-size: 1rem;
    }

    .lesson-nav {
        flex-direction: column;
        gap: var(--space-md);
    }

    .lesson-nav .btn-nav {
        width: 100%;
        justify-content: center;
    }
}

/* ============================
   SCROLLBAR
   ============================ */
::-webkit-scrollbar {
    width: 6px;
}

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background: var(--color-text-muted);
    border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--color-text-secondary);
}

/* ============================
   ANIMATIONS
   ============================ */
.fade-in {
    animation: fadeIn 0.5s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0;
    }

    to {
        opacity: 1;
    }
}

.slide-in {
    animation: slideIn 0.4s ease;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-10px);
    }

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

/* Tooltip */
.tooltip-trigger {
    position: relative;
    cursor: help;
    border-bottom: 1px dashed var(--color-primary-light);
    color: var(--color-primary-light);
}

.tooltip-trigger:hover::after {
    content: attr(data-tooltip);
    position: absolute;
    bottom: 100%;
    left: 50%;
    transform: translateX(-50%);
    background: var(--color-bg-elevated);
    border: 1px solid var(--color-border);
    padding: var(--space-sm) var(--space-md);
    border-radius: var(--radius-sm);
    font-size: 0.82rem;
    color: var(--color-text);
    white-space: nowrap;
    z-index: 10;
    box-shadow: var(--shadow-md);
    animation: feedbackSlide 0.2s ease;
}

/* Key Concept callout */
.key-concept {
    background: var(--gradient-hero);
    border: 1px solid rgba(108, 92, 231, 0.2);
    border-radius: var(--radius-lg);
    padding: var(--space-xl);
    margin-bottom: var(--space-xl);
    position: relative;
    overflow: hidden;
}

.key-concept::before {
    content: '💡';
    position: absolute;
    top: -10px;
    right: -10px;
    font-size: 5rem;
    opacity: 0.08;
}

.key-concept h3 {
    font-size: 1.1rem;
    font-weight: 700;
    color: var(--color-primary-light);
    margin-bottom: var(--space-sm);
}

.key-concept p {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
    margin: 0;
}

/* Tab component */
.tabs {
    margin-bottom: var(--space-xl);
}

.tab-headers {
    display: flex;
    gap: var(--space-xs);
    border-bottom: 1px solid var(--color-border);
    margin-bottom: var(--space-lg);
}

.tab-header {
    padding: var(--space-sm) var(--space-lg);
    background: none;
    border: none;
    color: var(--color-text-muted);
    font-family: var(--font-main);
    font-size: 0.9rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    border-bottom: 2px solid transparent;
    margin-bottom: -1px;
}

.tab-header:hover {
    color: var(--color-text);
}

.tab-header.active {
    color: var(--color-primary-light);
    border-bottom-color: var(--color-primary);
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

/* Accordion */
.accordion {
    margin-bottom: var(--space-xl);
}

.accordion-item {
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    margin-bottom: var(--space-sm);
    overflow: hidden;
}

.accordion-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: var(--space-md) var(--space-lg);
    background: var(--color-bg-card);
    cursor: pointer;
    transition: all var(--transition-fast);
    font-weight: 600;
    font-size: 0.95rem;
    color: var(--color-text);
}

.accordion-header:hover {
    background: var(--color-bg-hover);
}

.accordion-chevron {
    font-size: 0.8rem;
    color: var(--color-text-muted);
    transition: transform var(--transition-fast);
}

.accordion-item.open .accordion-chevron {
    transform: rotate(180deg);
}

.accordion-body {
    max-height: 0;
    overflow: hidden;
    transition: max-height var(--transition-slow);
}

.accordion-item.open .accordion-body {
    max-height: 500px;
}

.accordion-body-content {
    padding: var(--space-lg);
    font-size: 0.95rem;
    color: var(--color-text-secondary);
    line-height: 1.7;
}

/* Drag and drop sorting */
.sortable-list {
    list-style: none;
    padding: 0;
    margin-bottom: var(--space-xl);
}

.sortable-item {
    display: flex;
    align-items: center;
    gap: var(--space-md);
    padding: var(--space-md) var(--space-lg);
    background: var(--color-bg-card);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    margin-bottom: var(--space-sm);
    cursor: grab;
    transition: all var(--transition-fast);
    user-select: none;
}

.sortable-item:hover {
    border-color: var(--color-border-active);
}

.sortable-item:active {
    cursor: grabbing;
    background: var(--color-bg-hover);
    box-shadow: var(--shadow-md);
}

.sortable-item .drag-handle {
    color: var(--color-text-muted);
    font-size: 1rem;
}

.sortable-item .item-text {
    font-size: 0.95rem;
    color: var(--color-text-secondary);
}