/* ── Design System ── */
:root {
    --bg: #08080e;
    --bg-elevated: #0b0b14;
    --bg-card: rgba(255,255,255,.03);
    --bg-card-hover: rgba(255,255,255,.06);
    --text-primary: #f1f0ed;
    --text-secondary: rgba(241,240,237,.65);
    --text-tertiary: rgba(241,240,237,.4);
    --accent: #14b8a6;
    --accent-hover: #0d9488;
    --accent-dim: rgba(20,184,166,.12);
    --accent-alt: #f9735c;
    --border: rgba(255,255,255,.07);
    --border-accent: rgba(20,184,166,.25);
    --radius-sm: 8px;
    --radius-md: 14px;
    --radius-lg: 20px;
    --shadow-card: 0 2px 16px rgba(0,0,0,.2), inset 0 1px 0 rgba(255,255,255,.04);
    --shadow-hover: 0 8px 32px rgba(0,0,0,.3), inset 0 1px 0 rgba(255,255,255,.06);
    --shadow-lg: 0 20px 60px rgba(0,0,0,.4);
    --transition: .3s cubic-bezier(.16,1,.3,1);
    --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
    --nav-height: 64px;
    --color-chatgpt: #14b8a6;
    --color-prompt: #8b5cf6;
    --color-tools: #f59e0b;
    --color-nocode: #ec4899;
}

/* ── Reset ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-font-smoothing: antialiased; }
body {
    font-family: var(--font-sans);
    background: var(--bg);
    color: var(--text-primary);
    line-height: 1.7;
    font-size: 1rem;
    overflow-x: hidden;
    min-height: 100vh;
}

/* ── Ambient Background ── */
body::before {
    content: '';
    position: fixed; inset: 0; z-index: -1; pointer-events: none;
    background:
        radial-gradient(ellipse 80% 60% at 15% 15%, rgba(20,184,166,.06) 0%, transparent 60%),
        radial-gradient(ellipse 70% 50% at 85% 75%, rgba(249,115,92,.04) 0%, transparent 50%);
}
#app { min-height: 100vh; display: flex; flex-direction: column; }

/* ── Navigation ── */
.nav {
    position: sticky; top: 0; z-index: 100;
    background: rgba(8,8,14,.8); backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--border);
}
.nav-inner {
    max-width: 1200px; margin: 0 auto;
    display: flex; align-items: center; justify-content: space-between;
    height: var(--nav-height); padding: 0 1.5rem;
}
.nav-logo {
    font-size: 1.15rem; font-weight: 800; text-decoration: none;
    color: var(--text-primary); display: flex; align-items: center; gap: .5rem;
}
.nav-logo span { color: var(--accent); }
.nav-links { display: flex; align-items: center; gap: 1.5rem; }
.nav-links a {
    color: var(--text-secondary); text-decoration: none;
    font-size: .85rem; font-weight: 500;
    transition: color var(--transition); position: relative;
    padding: .3rem 0;
}
.nav-links a:hover, .nav-links a.active { color: var(--text-primary); }
.nav-links a.active::after {
    content: ''; position: absolute; bottom: -2px; left: 0; right: 0;
    height: 2px; background: var(--accent); border-radius: 2px;
}
.nav-user {
    display: flex; align-items: center; gap: .75rem;
}
.nav-user-name {
    font-size: .85rem; color: var(--text-secondary);
}
.btn-login, .btn-signup {
    padding: .4rem 1rem; border-radius: var(--radius-sm);
    font-size: .82rem; font-weight: 600; cursor: pointer;
    transition: all var(--transition); text-decoration: none;
}
.btn-login {
    background: transparent; color: var(--text-primary);
    border: 1px solid var(--border);
}
.btn-login:hover { border-color: var(--text-tertiary); }
.btn-signup {
    background: var(--accent); color: #08080e;
    border: none;
}
.btn-signup:hover { background: var(--accent-hover); }
.nav-toggle {
    display: none; background: none; border: none;
    color: var(--text-primary); cursor: pointer; padding: .25rem;
}

/* ── Main Content ── */
.main {
    flex: 1; padding: 2rem 1.5rem;
}
.main-inner {
    max-width: 1200px; margin: 0 auto;
}

/* ── Hero Section ── */
.hero {
    text-align: center; padding: 4rem 0 3rem;
}
.hero h1 {
    font-size: clamp(2.2rem, 5vw, 3.5rem);
    font-weight: 800; line-height: 1.1;
    letter-spacing: -.03em;
    margin-bottom: .75rem;
}
.hero h1 em { font-style: normal; color: var(--accent); }
.hero p {
    font-size: 1.05rem; color: var(--text-secondary);
    max-width: 600px; margin: 0 auto 2rem;
    line-height: 1.65;
}
.hero-cta { display: flex; gap: 1rem; justify-content: center; flex-wrap: wrap; }
.hero-stats {
    display: flex; justify-content: center; gap: 3rem;
    margin-top: 3rem; padding-top: 2rem;
    border-top: 1px solid var(--border);
}
.hero-stat { text-align: center; }
.hero-stat-num {
    font-size: 1.5rem; font-weight: 800; color: var(--accent);
    font-variant-numeric: tabular-nums;
}
.hero-stat-label { font-size: .8rem; color: var(--text-tertiary); margin-top: .2rem; }

/* ── Continue Learning ── */
.section-title {
    font-size: 1.4rem; font-weight: 700;
    margin-bottom: .5rem; letter-spacing: -.02em;
}
.section-sub {
    color: var(--text-secondary); font-size: .95rem;
    margin-bottom: 1.5rem;
}
.section-header {
    display: flex; align-items: center; justify-content: space-between;
    margin-bottom: 1.5rem;
}
.section-header h2 { font-size: 1.3rem; font-weight: 700; }
.section-header a {
    color: var(--accent); text-decoration: none;
    font-size: .88rem; font-weight: 600;
    transition: opacity var(--transition);
}
.section-header a:hover { opacity: .8; }

/* ── Course Cards ── */
.course-grid {
    display: grid; grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
    gap: 1rem; margin-bottom: 2rem;
}
.course-card {
    background: var(--bg-card); border: 1px solid var(--border);
    border-radius: var(--radius-md); overflow: hidden;
    transition: all var(--transition); cursor: pointer;
    text-decoration: none; color: inherit;
    display: flex; flex-direction: column;
}
.course-card:hover {
    border-color: var(--border-accent);
    background: var(--bg-card-hover);
    transform: translateY(-2px);
    box-shadow: var(--shadow-hover);
}
.course-card-top {
    padding: 1.5rem 1.5rem .75rem;
}
.course-card-icon {
    width: 40px; height: 40px; border-radius: 10px;
    display: flex; align-items: center; justify-content: center;
    font-size: 1.2rem; margin-bottom: .75rem;
}
.course-card h3 {
    font-size: 1.05rem; font-weight: 700;
    margin-bottom: .25rem;
}
.course-card p {
    color: var(--text-tertiary); font-size: .82rem;
    line-height: 1.5;
}
.course-card-meta {
    display: flex; gap: 1rem; padding: .75rem 1.5rem 1.25rem;
    border-top: 1px solid var(--border); margin-top: auto;
}
.course-card-meta span {
    display: flex; align-items: center; gap: .35rem;
    font-size: .78rem; color: var(--text-tertiary);
}
.course-card-progress {
    padding: 0 1.5rem 1rem;
}
.progress-bar {
    height: 4px; background: rgba(255,255,255,.06);
    border-radius: 4px; overflow: hidden;
}
.progress-fill {
    height: 100%; border-radius: 4px;
    background: var(--accent); transition: width .5s ease;
}
.progress-label {
    font-size: .72rem; color: var(--text-tertiary);
    margin-top: .35rem;
}

/* ── Buttons ── */
.btn {
    display: inline-flex; align-items: center; gap: .5rem;
    padding: .7rem 1.4rem; border-radius: var(--radius-sm);
    font-weight: 600; font-size: .9rem;
    cursor: pointer; border: none;
    text-decoration: none;
    transition: all var(--transition);
    line-height: 1;
}
.btn-primary {
    background: var(--accent); color: #08080e;
}
.btn-primary:hover { background: var(--accent-hover); transform: translateY(-1px); }
.btn-secondary {
    background: var(--bg-card); color: var(--text-primary);
    border: 1px solid var(--border);
}
.btn-secondary:hover { background: var(--bg-card-hover); }
.btn-lg { padding: .9rem 1.8rem; font-size: 1rem; }
.btn-sm { padding: .4rem .85rem; font-size: .8rem; }
.btn-ghost {
    background: transparent; color: var(--text-secondary);
    border: 1px solid transparent;
}
.btn-ghost:hover { color: var(--text-primary); background: var(--bg-card); }
.btn-block { width: 100%; justify-content: center; }

/* ── Course Detail ── */
.course-header {
    display: flex; gap: 2rem; padding: 2rem 0;
    border-bottom: 1px solid var(--border);
    margin-bottom: 2rem;
}
.course-header-info { flex: 1; }
.course-header-info h1 {
    font-size: clamp(1.5rem, 3vw, 2.2rem);
    font-weight: 800; letter-spacing: -.02em;
    margin-bottom: .25rem;
}
.course-header-info .subtitle {
    font-size: 1rem; color: var(--text-secondary);
    margin-bottom: .75rem;
}
.course-header-info .desc {
    color: var(--text-tertiary); font-size: .9rem;
    line-height: 1.6; margin-bottom: 1.25rem;
}
.course-tags {
    display: flex; gap: .75rem; flex-wrap: wrap;
    margin-bottom: 1.25rem;
}
.course-tag {
    padding: .25rem .75rem; border-radius: 100px;
    font-size: .72rem; font-weight: 600;
    background: var(--accent-dim); color: var(--accent);
    border: 1px solid var(--border-accent);
}
.course-header-cta {
    display: flex; gap: .75rem; align-items: center;
}
.course-price-large {
    font-size: 1.5rem; font-weight: 900; color: var(--accent);
}
.course-sidebar {
    width: 220px; flex-shrink: 0;
}

/* ── Syllabus ── */
.syllabus { margin-bottom: 2rem; }
.syllabus h2 { font-size: 1.2rem; font-weight: 700; margin-bottom: 1rem; }
.chapter {
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    margin-bottom: .5rem;
    overflow: hidden;
}
.chapter-header {
    display: flex; align-items: center; justify-content: space-between;
    padding: 1rem 1.25rem; background: var(--bg-card);
    cursor: pointer; user-select: none;
    transition: background var(--transition);
}
.chapter-header:hover { background: var(--bg-card-hover); }
.chapter-header-left { display: flex; align-items: center; gap: .75rem; }
.chapter-num {
    width: 28px; height: 28px; border-radius: 8px;
    display: flex; align-items: center; justify-content: center;
    font-weight: 700; font-size: .75rem;
    background: var(--accent-dim); color: var(--accent);
    flex-shrink: 0;
}
.chapter-header h3 { font-size: .92rem; font-weight: 600; }
.chapter-progress-small { font-size: .75rem; color: var(--text-tertiary); }
.chapter-toggle {
    transition: transform var(--transition); color: var(--text-tertiary);
}
.chapter.open .chapter-toggle { transform: rotate(180deg); }
.chapter-body { display: none; }
.chapter.open .chapter-body { display: block; }
.lesson-item {
    display: flex; align-items: center; gap: .75rem;
    padding: .75rem 1.25rem .75rem 3rem;
    border-top: 1px solid var(--border);
    cursor: pointer; transition: background var(--transition);
    text-decoration: none; color: inherit;
}
.lesson-item:hover { background: var(--bg-card); }
.lesson-status {
    width: 20px; height: 20px; border-radius: 50%;
    border: 2px solid var(--text-tertiary); flex-shrink: 0;
    display: flex; align-items: center; justify-content: center;
    transition: all var(--transition);
}
.lesson-status.completed {
    background: var(--accent); border-color: var(--accent);
}
.lesson-status.completed::after {
    content: '✓'; color: #08080e; font-size: 11px; font-weight: 800;
}
.lesson-status.in-progress {
    border-color: var(--accent);
    background: var(--accent-dim);
}
.lesson-info { flex: 1; min-width: 0; }
.lesson-title { font-size: .88rem; font-weight: 500; }
.lesson-type {
    font-size: .72rem; color: var(--text-tertiary);
    text-transform: capitalize;
}
.lesson-duration {
    font-size: .78rem; color: var(--text-tertiary);
    white-space: nowrap;
}

/* ── Lesson View ── */
.lesson-view {
    max-width: 800px; margin: 0 auto;
}
.lesson-nav {
    display: flex; justify-content: space-between; align-items: center;
    padding: .5rem 0 1rem; margin-bottom: 1rem;
    border-bottom: 1px solid var(--border);
}
.lesson-nav-back {
    display: flex; align-items: center; gap: .35rem;
    color: var(--text-secondary); text-decoration: none;
    font-size: .85rem; font-weight: 500;
    transition: color var(--transition);
}
.lesson-nav-back:hover { color: var(--text-primary); }
.lesson-nav-info { text-align: center; }
.lesson-nav-info h1 {
    font-size: 1.1rem; font-weight: 700;
    line-height: 1.3;
}
.lesson-nav-info .course-name {
    font-size: .78rem; color: var(--accent); font-weight: 600;
}
.lesson-nav-actions { display: flex; gap: .5rem; }

/* ── Lesson Content ── */
.lesson-content {
    padding: 1.5rem 0;
    font-size: .95rem; line-height: 1.8;
    color: var(--text-primary);
}
.lesson-content h2 {
    font-size: 1.4rem; font-weight: 700;
    margin: 2rem 0 .75rem; letter-spacing: -.02em;
}
.lesson-content h3 {
    font-size: 1.1rem; font-weight: 600;
    margin: 1.5rem 0 .5rem;
}
.lesson-content p {
    margin-bottom: 1rem; color: var(--text-secondary);
}
.lesson-content ul, .lesson-content ol {
    margin: .5rem 0 1rem 1.5rem;
    color: var(--text-secondary);
}
.lesson-content li { margin-bottom: .35rem; }
.lesson-content strong { color: var(--text-primary); font-weight: 600; }
.lesson-content code {
    font-family: var(--font-mono);
    background: rgba(255,255,255,.05);
    padding: .15rem .4rem; border-radius: 4px;
    font-size: .85em;
}
.lesson-content pre {
    background: rgba(255,255,255,.03);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 1rem 1.25rem;
    overflow-x: auto;
    margin: 1rem 0;
}
.lesson-content pre code {
    background: none; padding: 0;
    font-size: .82rem; line-height: 1.6;
}
.tip-box {
    background: var(--accent-dim);
    border: 1px solid var(--border-accent);
    border-radius: var(--radius-sm);
    padding: 1rem 1.25rem;
    margin: 1.25rem 0;
}
.tip-box strong {
    color: var(--accent); display: block;
    margin-bottom: .25rem; font-size: .85rem;
    text-transform: uppercase; letter-spacing: .05em;
}
.tip-box p { margin-bottom: 0; font-size: .9rem; }
.exercise-box {
    background: rgba(139,92,246,.08);
    border: 1px solid rgba(139,92,246,.2);
    border-radius: var(--radius-sm);
    padding: 1.25rem;
    margin: 1.5rem 0;
}
.exercise-box h3 {
    font-size: 1rem; color: #a78bfa; margin-top: 0;
}
.exercise-box p { font-size: .9rem; }
.exercise-area {
    margin: 1rem 0;
}
.exercise-area textarea {
    width: 100%; min-height: 120px;
    background: rgba(255,255,255,.03);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    padding: .75rem;
    font-family: var(--font-sans);
    font-size: .9rem;
    resize: vertical;
    transition: border-color var(--transition);
}
.exercise-area textarea:focus {
    outline: none; border-color: var(--accent);
}
.exercise-feedback {
    margin-top: 1rem;
    padding: 1rem;
    border-radius: var(--radius-sm);
    font-size: .88rem;
    display: none;
}
.exercise-feedback.show { display: block; }
.exercise-feedback.good {
    background: rgba(20,184,166,.1);
    border: 1px solid var(--border-accent);
    color: var(--accent);
}
.exercise-feedback.hint {
    background: rgba(139,92,246,.1);
    border: 1px solid rgba(139,92,246,.2);
    color: #a78bfa;
}

/* ── Quiz ── */
.quiz-question {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 1.25rem;
    margin: 1rem 0;
}
.quiz-question p { font-weight: 600; margin-bottom: .75rem; font-size: .92rem; }
.quiz-option {
    display: flex; align-items: center; gap: .5rem;
    padding: .6rem .75rem;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: background var(--transition);
    margin-bottom: .25rem;
}
.quiz-option:hover { background: var(--bg-card-hover); }
.quiz-option input[type="radio"] {
    accent-color: var(--accent);
}
.quiz-option label {
    cursor: pointer; font-size: .88rem;
    color: var(--text-secondary); flex: 1;
}
.quiz-result {
    padding: .75rem; margin-top: .5rem;
    border-radius: var(--radius-sm);
    font-size: .85rem;
    display: none;
}
.quiz-result.correct {
    display: block;
    background: rgba(20,184,166,.1);
    color: var(--accent);
}
.quiz-result.incorrect {
    display: block;
    background: rgba(249,115,92,.1);
    color: var(--accent-alt);
}

/* ── Lesson Complete ── */
.lesson-complete-bar {
    display: flex; align-items: center; justify-content: space-between;
    padding: 1rem 1.5rem;
    background: var(--accent-dim);
    border: 1px solid var(--border-accent);
    border-radius: var(--radius-md);
    margin: 2rem 0;
}
.lesson-complete-bar span {
    font-size: .9rem; font-weight: 600; color: var(--accent);
}

/* ── Auth ── */
.auth-page {
    max-width: 420px; margin: 3rem auto;
    padding: 2rem;
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
}
.auth-page h1 {
    font-size: 1.5rem; font-weight: 800;
    text-align: center; margin-bottom: .25rem;
}
.auth-page .subtitle {
    text-align: center; color: var(--text-secondary);
    font-size: .9rem; margin-bottom: 2rem;
}
.form-group {
    margin-bottom: 1.25rem;
}
.form-group label {
    display: block; font-size: .85rem; font-weight: 600;
    margin-bottom: .35rem; color: var(--text-secondary);
}
.form-group input {
    width: 100%; padding: .7rem .85rem;
    background: rgba(255,255,255,.03);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: var(--font-sans); font-size: .9rem;
    transition: border-color var(--transition);
}
.form-group input:focus {
    outline: none; border-color: var(--accent);
}
.form-error {
    color: var(--accent-alt); font-size: .82rem;
    margin-top: .35rem; display: none;
}
.auth-divider {
    text-align: center; color: var(--text-tertiary);
    font-size: .82rem; margin: 1.5rem 0;
    display: flex; align-items: center; gap: 1rem;
}
.auth-divider::before, .auth-divider::after {
    content: ''; flex: 1; height: 1px; background: var(--border);
}
.auth-alt {
    text-align: center; margin-top: 1rem;
    font-size: .85rem; color: var(--text-secondary);
}
.auth-alt a { color: var(--accent); text-decoration: none; font-weight: 600; }
.auth-alt a:hover { text-decoration: underline; }

/* ── Profile ── */
.profile-page {
    max-width: 700px; margin: 0 auto;
}
.profile-header {
    display: flex; align-items: center; gap: 1.5rem;
    padding-bottom: 2rem; border-bottom: 1px solid var(--border);
    margin-bottom: 2rem;
}
.profile-avatar {
    width: 64px; height: 64px; border-radius: 50%;
    background: var(--accent-dim); color: var(--accent);
    display: flex; align-items: center; justify-content: center;
    font-size: 1.5rem; font-weight: 800;
}
.profile-info h2 { font-size: 1.3rem; font-weight: 700; }
.profile-info .email { color: var(--text-tertiary); font-size: .88rem; }
.profile-stats {
    display: grid; grid-template-columns: repeat(3, 1fr);
    gap: 1rem; margin-bottom: 2rem;
}
.profile-stat {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 1rem; text-align: center;
}
.profile-stat-num {
    font-size: 1.3rem; font-weight: 800; color: var(--accent);
}
.profile-stat-label { font-size: .78rem; color: var(--text-tertiary); margin-top: .2rem; }

/* ── empty state ── */
.empty-state {
    text-align: center; padding: 3rem 1rem;
    color: var(--text-tertiary);
}
.empty-state .icon { font-size: 2.5rem; margin-bottom: 1rem; }
.empty-state h3 { font-size: 1.1rem; font-weight: 600; color: var(--text-secondary); margin-bottom: .5rem; }
.empty-state p { font-size: .9rem; max-width: 400px; margin: 0 auto 1.5rem; }

/* ── Footer ── */
.footer {
    border-top: 1px solid var(--border);
    padding: 2rem 1.5rem; text-align: center;
}
.footer p { color: var(--text-tertiary); font-size: .82rem; }
.footer a { color: var(--accent); text-decoration: none; }

/* ── Toast ── */
.toast {
    position: fixed; bottom: 1.5rem; right: 1.5rem;
    padding: .85rem 1.25rem;
    border-radius: var(--radius-sm);
    font-size: .88rem; font-weight: 600;
    z-index: 1000;
    opacity: 0; transform: translateY(10px);
    transition: all .3s ease;
    pointer-events: none;
}
.toast.show { opacity: 1; transform: translateY(0); }
.toast.success { background: rgba(20,184,166,.9); color: #08080e; }
.toast.error { background: rgba(249,115,92,.9); color: #08080e; }

/* ── Loading ── */
.loading {
    display: flex; align-items: center; justify-content: center;
    padding: 4rem; color: var(--text-tertiary);
}
.spinner { animation: spin .8s linear infinite; font-size: 1.5rem; }
@keyframes spin { 100% { transform: rotate(360deg); } }

/* ── Responsive ── */
@media (max-width: 768px) {
    .nav-links { display: none; }
    .nav-toggle { display: block; }
    .nav-links.open {
        display: flex; flex-direction: column;
        position: absolute; top: var(--nav-height); left: 0; right: 0;
        background: rgba(8,8,14,.95); backdrop-filter: blur(20px);
        border-bottom: 1px solid var(--border);
        padding: 1rem 1.5rem; gap: .75rem;
    }
    .course-header { flex-direction: column; }
    .course-sidebar { width: 100%; }
    .hero-stats { flex-wrap: wrap; gap: 1.5rem; }
    .profile-stats { grid-template-columns: repeat(2, 1fr); }
    .lesson-nav { flex-direction: column; gap: .5rem; text-align: center; }
    .course-grid { grid-template-columns: 1fr; }
    .lesson-nav-actions { width: 100%; justify-content: center; }
}