:root {
    --bg: #0a1208;
    --bg-soft: #121f10;
    --panel: rgba(18, 32, 16, 0.92);
    --card: rgba(255, 255, 255, 0.97);
    --card-soft: rgba(236, 248, 232, 0.94);
    --text: #0f1a0c;
    --text-soft: #3d5238;
    --light: #eef8e8;
    --accent: #4ade80;
    --accent-strong: #16a34a;
    --accent-soft: #dcfce7;
    --amber: #fbbf24;
    --danger: #dc2626;
    --border: rgba(18, 38, 20, 0.12);
    --shadow: 0 24px 60px rgba(4, 13, 8, 0.35);
    --radius-xl: 28px;
    --radius-lg: 20px;
    --radius-md: 14px;
    --radius-sm: 10px;
    --mono: "JetBrains Mono", "Cascadia Code", Consolas, monospace;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
    margin: 0;
    font-family: "Source Sans 3", "Segoe UI", Arial, sans-serif;
    font-size: 1.05rem;
    line-height: 1.65;
    color: var(--text);
    background:
        radial-gradient(circle at 12% 0%, rgba(74, 222, 128, 0.18), transparent 28%),
        radial-gradient(circle at 88% 8%, rgba(251, 191, 36, 0.12), transparent 22%),
        linear-gradient(180deg, #081008 0%, #0f1a12 100%);
    min-height: 100vh;
}

a { color: var(--accent-strong); }

.site-nav {
    position: sticky;
    top: 0;
    z-index: 40;
    background: rgba(8, 16, 10, 0.94);
    border-bottom: 1px solid rgba(255, 255, 255, 0.08);
    backdrop-filter: blur(10px);
}

.site-nav__bar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    flex-wrap: wrap;
    gap: 10px;
    padding: 12px 0;
}

.site-shell {
    width: min(1120px, calc(100% - 32px));
    margin: 0 auto;
}

.site-nav__brand {
    font-weight: 800;
    color: var(--light);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 8px;
}

.site-nav__brand i { color: var(--accent); }

.site-nav__links {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    align-items: center;
}

.site-nav__links a {
    text-decoration: none;
    color: rgba(232, 248, 232, 0.9);
    font-weight: 600;
    font-size: 0.9rem;
    padding: 7px 13px;
    border-radius: 999px;
    border: 1px solid rgba(255, 255, 255, 0.1);
    background: rgba(255, 255, 255, 0.05);
}

.site-nav__links a:hover,
.site-nav__links a[aria-current="page"] {
    background: rgba(74, 222, 128, 0.22);
    border-color: rgba(74, 222, 128, 0.35);
    color: white;
}

.lang-switch {
    display: flex;
    align-items: center;
    gap: 6px;
    color: var(--light);
    font-size: 0.88rem;
}

.lang-switch select {
    background: rgba(255, 255, 255, 0.08);
    color: var(--light);
    border: 1px solid rgba(255, 255, 255, 0.15);
    border-radius: 8px;
    padding: 5px 8px;
}

.hero {
    margin: 28px 0 24px;
    padding: 32px;
    border-radius: var(--radius-xl);
    background: linear-gradient(135deg, rgba(22, 163, 74, 0.25), rgba(15, 26, 12, 0.85));
    border: 1px solid rgba(74, 222, 128, 0.2);
    color: var(--light);
    box-shadow: var(--shadow);
}

.hero .eyebrow {
    display: inline-block;
    font-size: 0.78rem;
    font-weight: 700;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--accent);
    margin-bottom: 8px;
}

.hero h1 {
    margin: 0 0 12px;
    font-size: clamp(1.8rem, 4vw, 2.6rem);
    line-height: 1.15;
}

.hero p { margin: 0; max-width: 62ch; opacity: 0.92; }

.hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-top: 22px;
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 11px 18px;
    border-radius: 999px;
    font-weight: 700;
    font-size: 0.95rem;
    text-decoration: none;
    border: none;
    cursor: pointer;
    transition: transform 0.12s ease, box-shadow 0.12s ease;
}

.btn:hover { transform: translateY(-1px); }

.btn-primary {
    background: linear-gradient(135deg, #22c55e, #16a34a);
    color: #052e16;
    box-shadow: 0 8px 24px rgba(34, 197, 94, 0.35);
}

.btn-secondary {
    background: rgba(255, 255, 255, 0.12);
    color: var(--light);
    border: 1px solid rgba(255, 255, 255, 0.18);
}

.btn-soft {
    background: var(--card-soft);
    color: var(--text);
    border: 1px solid var(--border);
}

.menu-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 16px;
    margin-bottom: 40px;
}

.menu-card {
    display: block;
    padding: 22px;
    border-radius: var(--radius-lg);
    background: var(--card);
    border: 1px solid var(--border);
    text-decoration: none;
    color: inherit;
    box-shadow: var(--shadow);
    transition: border-color 0.15s, transform 0.15s;
}

.menu-card:hover {
    border-color: rgba(34, 197, 94, 0.45);
    transform: translateY(-2px);
}

.menu-card h2 { margin: 8px 0; font-size: 1.25rem; }
.menu-card p { margin: 0; color: var(--text-soft); font-size: 0.95rem; }

.pill {
    display: inline-block;
    font-size: 0.72rem;
    font-weight: 800;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    padding: 4px 10px;
    border-radius: 999px;
    background: var(--accent-soft);
    color: var(--accent-strong);
}

.chapter-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 14px;
    margin-bottom: 36px;
}

.chapter-card {
    padding: 18px;
    border-radius: var(--radius-md);
    background: var(--card);
    border: 1px solid var(--border);
    text-decoration: none;
    color: inherit;
    position: relative;
}

.chapter-card:hover { border-color: var(--accent-strong); }

.chapter-card.done::after {
    content: "✓";
    position: absolute;
    top: 12px;
    right: 12px;
    width: 26px;
    height: 26px;
    border-radius: 50%;
    background: var(--accent-soft);
    color: var(--accent-strong);
    display: grid;
    place-items: center;
    font-weight: 800;
    font-size: 0.85rem;
}

.chapter-num {
    font-family: var(--mono);
    font-size: 0.8rem;
    color: var(--accent-strong);
    font-weight: 700;
}

.lesson-panel {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    padding: 22px;
    margin-bottom: 16px;
    box-shadow: var(--shadow);
}

.lesson-panel h2 { margin-top: 0; }

.lesson-panel h3 { margin: 1.2em 0 0.4em; color: var(--accent-strong); }

.formula-box {
    font-family: var(--mono);
    background: #0f1a12;
    color: #bbf7d0;
    padding: 14px 18px;
    border-radius: var(--radius-sm);
    margin: 12px 0;
    font-size: 1rem;
}

.key-list {
    margin: 0;
    padding-left: 1.2rem;
}

.key-list li { margin-bottom: 6px; }

.quiz-block {
    margin-top: 14px;
    padding: 16px;
    border-radius: var(--radius-md);
    background: var(--card-soft);
    border: 1px dashed rgba(34, 197, 94, 0.35);
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 8px;
    margin: 12px 0;
}

.quiz-option {
    text-align: left;
    padding: 10px 14px;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
    background: white;
    cursor: pointer;
    font: inherit;
}

.quiz-option.is-selected { border-color: var(--accent-strong); background: var(--accent-soft); }
.quiz-option.is-correct { border-color: #16a34a; background: #dcfce7; }
.quiz-option.is-wrong { border-color: var(--danger); background: #fee2e2; }

.feedback {
    font-weight: 700;
    min-height: 1.4em;
}

.feedback.ok { color: #15803d; }
.feedback.err { color: var(--danger); }

.calc-widget {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
    gap: 12px;
    align-items: end;
    margin: 14px 0;
}

.calc-widget label {
    display: flex;
    flex-direction: column;
    gap: 4px;
    font-size: 0.88rem;
    font-weight: 600;
}

.calc-widget input,
.calc-widget select {
    padding: 9px 11px;
    border-radius: 8px;
    border: 1px solid var(--border);
    font: inherit;
}

.calc-result {
    font-family: var(--mono);
    font-size: 1.1rem;
    color: var(--accent-strong);
    margin-top: 8px;
}

.exam-progress {
    height: 8px;
    background: rgba(255, 255, 255, 0.15);
    border-radius: 999px;
    overflow: hidden;
    margin: 16px 0;
}

.exam-progress__bar {
    height: 100%;
    background: linear-gradient(90deg, #22c55e, #fbbf24);
    transition: width 0.25s ease;
}

.exam-score {
    font-size: 2rem;
    font-weight: 800;
    color: var(--accent-strong);
}

.exam-score.fail { color: var(--danger); }

.glossary-table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.95rem;
    background: var(--card);
    border-radius: var(--radius-md);
    overflow: hidden;
}

.glossary-table th,
.glossary-table td {
    padding: 10px 12px;
    border-bottom: 1px solid var(--border);
    text-align: left;
}

.glossary-table th {
    background: var(--card-soft);
    font-size: 0.82rem;
    text-transform: uppercase;
    letter-spacing: 0.06em;
}

.footer-note {
    color: rgba(232, 248, 232, 0.65);
    font-size: 0.88rem;
    margin: 32px 0 48px;
}

.lesson-nav {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: space-between;
    margin: 24px 0 40px;
}

.progress-bar-wrap {
    margin: 8px 0 20px;
    color: var(--light);
    font-size: 0.9rem;
}

@media (max-width: 640px) {
    .hero { padding: 22px; }
    .site-nav__links a { padding: 6px 10px; font-size: 0.82rem; }
}