:root {
  --bg: #0d0f14;
  --bg2: #13161e;
  --bg3: #1a1e28;
  --card: #1e2330;
  --border: #2a2f3e;
  --border2: #353c52;
  --accent: #4f8ef7;
  --accent2: #7c5fe6;
  --green: #3ecf8e;
  --yellow: #f5c842;
  --red: #f75c5c;
  --text: #e8eaf0;
  --text2: #9da3b4;
  --text3: #5c6278;
  --mono: 'IBM Plex Mono', monospace;
}

/* ── FONT SCALE TOÀN CỤC ──────────────────────────────────
   Thay đổi GIÁ TRỊ DUY NHẤT này để scale toàn bộ font size.
   Tất cả font-size trong file này dùng rem (chuẩn 16px).
   Ví dụ: 17px → tăng ~6%  |  18px → tăng ~12.5%  |  16px → không đổi
   ──────────────────────────────────────────────────────── */
html { font-size: 17px; }

* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: 'IBM Plex Sans', sans-serif; background: var(--bg); color: var(--text); min-height: 100vh; }

/* ── LAYOUT ── */
.app { display: flex; height: 100vh; overflow: hidden; }
.sidebar { width: 280px; min-width: 280px; background: var(--bg2); border-right: 1px solid var(--border); display: flex; flex-direction: column; overflow-y: auto; }
.main { flex: 1; overflow-y: auto; }

/* ── SIDEBAR ── */
.sb-header { padding: 20px 18px 16px; border-bottom: 1px solid var(--border); }
.sb-logo { font-size: 0.6875rem; font-weight: 600; letter-spacing: 2px; color: var(--accent); text-transform: uppercase; margin-bottom: 4px; }
.sb-title { font-size: 0.9375rem; font-weight: 600; color: var(--text); line-height: 1.3; }
.sb-progress { margin: 12px 18px; }
.prog-bar { height: 3px; background: var(--border); border-radius: 2px; overflow: hidden; }
.prog-fill { height: 100%; background: linear-gradient(90deg, var(--accent), var(--accent2)); border-radius: 2px; transition: width .4s; }
.prog-label { font-size: 0.6875rem; color: var(--text3); margin-top: 5px; }

.sb-section { padding: 10px 18px 4px; font-size: 0.625rem; font-weight: 600; letter-spacing: 1.5px; color: var(--text3); text-transform: uppercase; }
.sb-item { display: flex; align-items: center; gap: 10px; padding: 9px 18px; cursor: pointer; border-left: 2px solid transparent; transition: all .15s; }
.sb-item:hover { background: var(--bg3); }
.sb-item.active { background: rgba(79,142,247,0.08); border-left-color: var(--accent); }
.sb-item.done .sb-dot { background: var(--green); }
.sb-dot { width: 6px; height: 6px; border-radius: 50%; background: var(--border2); flex-shrink: 0; transition: background .2s; }
.sb-item.active .sb-dot { background: var(--accent); }
.sb-item-text { font-size: 0.8125rem; color: var(--text2); line-height: 1.3; }
.sb-item.active .sb-item-text { color: var(--text); font-weight: 500; }
.sb-duration { font-size: 0.6875rem; color: var(--text3); margin-left: auto; font-family: var(--mono); }

/* ── MAIN CONTENT ── */
.lesson-hero { background: linear-gradient(135deg, #0d1829 0%, #151028 100%); border-bottom: 1px solid var(--border); padding: 36px 48px 32px; position: relative; overflow: hidden; }
.lesson-hero::before { content: ''; position: absolute; top: -60px; right: -60px; width: 300px; height: 300px; border-radius: 50%; background: radial-gradient(circle, rgba(79,142,247,0.08) 0%, transparent 70%); }
.hero-badge { display: inline-flex; align-items: center; gap: 6px; padding: 4px 10px; border-radius: 20px; border: 1px solid rgba(79,142,247,0.3); background: rgba(79,142,247,0.08); font-size: 0.6875rem; font-weight: 600; color: var(--accent); letter-spacing: 1px; text-transform: uppercase; margin-bottom: 12px; }
.hero-title { font-size: 1.625rem; font-weight: 700; line-height: 1.2; margin-bottom: 8px; }
.hero-sub { font-size: 0.875rem; color: var(--text2); max-width: 560px; line-height: 1.6; }
.hero-tags { display: flex; gap: 8px; margin-top: 16px; flex-wrap: wrap; }
.tag { padding: 4px 10px; border-radius: 6px; font-size: 0.6875rem; font-weight: 500; background: var(--bg3); border: 1px solid var(--border); color: var(--text2); }

.content-area { padding: 36px 48px; max-width: 900px; }

/* ── LESSON BLOCKS ── */
.block { margin-bottom: 28px; }
.block-title { font-size: 0.6875rem; font-weight: 600; letter-spacing: 1.5px; color: var(--text3); text-transform: uppercase; margin-bottom: 12px; display: flex; align-items: center; gap: 8px; }
.block-title::after { content: ''; flex: 1; height: 1px; background: var(--border); }

.concept-box { background: var(--card); border: 1px solid var(--border); border-radius: 10px; padding: 18px 20px; margin-bottom: 10px; }
.concept-box h3 { font-size: 0.9375rem; font-weight: 600; margin-bottom: 8px; }
.concept-box p { font-size: 0.8125rem; color: var(--text2); line-height: 1.7; }

.formula-box { background: #0a0e1a; border: 1px solid var(--border); border-left: 3px solid var(--accent); border-radius: 8px; padding: 14px 18px; font-family: var(--mono); font-size: 0.875rem; color: var(--accent); margin: 10px 0; }
.formula-box .label { font-size: 0.625rem; color: var(--text3); margin-bottom: 6px; letter-spacing: 1px; text-transform: uppercase; font-family: 'IBM Plex Sans', sans-serif; }

/* ── INTERACTIVE ── */
.interactive { background: var(--bg2); border: 1px solid var(--border); border-radius: 12px; overflow: hidden; margin: 16px 0; }
.int-header { padding: 14px 18px; border-bottom: 1px solid var(--border); display: flex; align-items: center; justify-content: space-between; }
.int-title { font-size: 0.8125rem; font-weight: 600; display: flex; align-items: center; gap: 8px; }
.int-badge { font-size: 0.625rem; font-weight: 600; padding: 2px 8px; border-radius: 4px; background: rgba(79,142,247,0.15); color: var(--accent); letter-spacing: 0.5px; }
.int-body { padding: 18px; }

.slider-row { display: flex; align-items: center; gap: 12px; margin-bottom: 12px; }
.slider-label { font-size: 0.75rem; color: var(--text2); min-width: 130px; }
input[type=range] { flex: 1; accent-color: var(--accent); cursor: pointer; }
.slider-val { font-family: var(--mono); font-size: 0.8125rem; font-weight: 500; min-width: 52px; text-align: right; color: var(--text); }

.metrics { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin: 14px 0; }
.metric { background: var(--bg); border: 1px solid var(--border); border-radius: 8px; padding: 12px 14px; text-align: center; }
.metric-label { font-size: 0.625rem; color: var(--text3); text-transform: uppercase; letter-spacing: 0.8px; margin-bottom: 4px; }
.metric-val { font-size: 1.25rem; font-weight: 600; font-family: var(--mono); }
.metric-val.ok { color: var(--green); }
.metric-val.warn { color: var(--yellow); }
.metric-val.bad { color: var(--red); }
.metric-val.info { color: var(--accent); }

/* ── METRIC CARD (lesson7/8) ── */
.metric-card { background: var(--bg); border: 1px solid var(--border); border-radius: 8px; padding: 12px 14px; }
.metric-card .metric-label { font-size: 0.625rem; color: var(--text3); text-transform: uppercase; letter-spacing: 0.8px; margin-bottom: 4px; display: block; }
.metric-card .metric-val { font-size: 1.25rem; font-weight: 600; font-family: var(--mono); }

canvas { display: block; width: 100% !important; }

.insight { background: rgba(79,142,247,0.06); border: 1px solid rgba(79,142,247,0.2); border-radius: 8px; padding: 12px 16px; font-size: 0.8125rem; color: var(--text2); line-height: 1.6; margin-top: 12px; }
.insight strong { color: var(--text); }

/* ── STEP CARDS ── */
.steps { display: flex; flex-direction: column; gap: 10px; margin: 12px 0; }
.step { display: flex; gap: 14px; align-items: flex-start; }
.step-num { width: 26px; height: 26px; border-radius: 50%; background: var(--accent); color: white; font-size: 0.75rem; font-weight: 700; display: flex; align-items: center; justify-content: center; flex-shrink: 0; margin-top: 2px; }
.step-content { flex: 1; }
.step-title { font-size: 0.8125rem; font-weight: 600; margin-bottom: 3px; }
.step-desc { font-size: 0.75rem; color: var(--text2); line-height: 1.5; }

/* ── SPSS TABLE ── */
.spss-table { width: 100%; border-collapse: collapse; font-size: 0.75rem; margin: 8px 0; font-family: var(--mono); }
.spss-table th { background: #1a1e2c; padding: 7px 10px; text-align: left; color: var(--text2); font-size: 0.6875rem; font-weight: 600; border: 1px solid var(--border); }
.spss-table td { padding: 6px 10px; border: 1px solid var(--border); color: var(--text); }
.spss-table tr:nth-child(even) { background: rgba(255,255,255,0.02); }
.spss-table .highlight { background: rgba(79,142,247,0.1); color: var(--accent); font-weight: 600; }
.spss-table .green { background: rgba(62,207,142,0.1); color: var(--green); font-weight: 600; }
.spss-table .red { background: rgba(247,92,92,0.1); color: var(--red); font-weight: 600; }

/* ── DECISION TREE ── */
.tree-node { background: var(--card); border: 1px solid var(--border); border-radius: 8px; padding: 10px 14px; font-size: 0.75rem; cursor: pointer; transition: all .15s; }
.tree-node:hover { border-color: var(--accent); background: rgba(79,142,247,0.06); }
.tree-node.selected { border-color: var(--green); background: rgba(62,207,142,0.06); color: var(--green); }
.tree-node.question { font-weight: 600; cursor: default; border-color: var(--border2); }
.tree-row { display: flex; gap: 8px; margin: 6px 0; flex-wrap: wrap; }
.tree-arrow { font-size: 0.6875rem; color: var(--text3); margin: 0 4px; }
.result-tag { display: inline-block; padding: 5px 14px; border-radius: 6px; font-size: 0.8125rem; font-weight: 600; background: rgba(62,207,142,0.12); color: var(--green); border: 1px solid rgba(62,207,142,0.3); }

/* ── NAV BUTTONS ── */
.lesson-nav { display: flex; justify-content: space-between; align-items: center; margin-top: 40px; padding-top: 24px; border-top: 1px solid var(--border); }
.btn { padding: 10px 22px; border-radius: 8px; border: none; font-size: 0.8125rem; font-weight: 600; cursor: pointer; transition: all .15s; font-family: 'IBM Plex Sans', sans-serif; }
.btn-secondary { background: var(--bg3); color: var(--text2); border: 1px solid var(--border); }
.btn-secondary:hover { border-color: var(--border2); color: var(--text); }
.btn-primary { background: var(--accent); color: white; }
.btn-primary:hover { background: #6ba3f9; }

/* ── 2×2 TABLE ── */
.cell-tp { background: rgba(62,207,142,0.15); color: var(--green); font-weight: 700; }
.cell-fp { background: rgba(247,92,92,0.15); color: var(--red); font-weight: 700; }
.cell-fn { background: rgba(245,200,66,0.15); color: var(--yellow); font-weight: 700; }
.cell-tn { background: rgba(79,142,247,0.15); color: var(--accent); font-weight: 700; }

/* ── BAYES DIAGNOSTIC ── */
.bayes-metric-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; margin: 14px 0; }
.bayes-metric-card { border: 1px solid var(--border); border-radius: 10px; padding: 14px 16px; background: var(--bg); }
.bayes-metric-card.col { border-top-width: 3px; }
.bayes-metric-card.col-se { border-top-color: var(--green); }
.bayes-metric-card.col-sp { border-top-color: var(--accent); }
.bayes-metric-card.row-ppv { border-top-width: 3px; border-top-color: var(--red); }
.bayes-metric-card.row-npv { border-top-width: 3px; border-top-color: var(--yellow); }
.bmc-title { font-size: 0.6875rem; font-weight: 700; letter-spacing: 1px; text-transform: uppercase; margin-bottom: 4px; }
.bmc-dir { font-size: 0.625rem; color: var(--text3); margin-bottom: 8px; }
.bmc-formula { font-family: var(--mono); font-size: 0.75rem; color: var(--text2); margin-bottom: 6px; background: var(--bg2); border-radius: 4px; padding: 6px 8px; }
.bmc-val { font-size: 1.375rem; font-weight: 700; font-family: var(--mono); }
.bmc-desc { font-size: 0.6875rem; color: var(--text3); margin-top: 4px; line-height: 1.4; }
.bayes-flow { display: flex; align-items: center; justify-content: center; gap: 10px; margin: 16px 0; flex-wrap: wrap; }
.bayes-flow-box { background: var(--card); border: 1px solid var(--border); border-radius: 8px; padding: 10px 16px; text-align: center; }
.bayes-flow-box .label { font-size: 0.625rem; color: var(--text3); text-transform: uppercase; letter-spacing: 0.8px; }
.bayes-flow-box .val  { font-size: 1.25rem; font-weight: 700; font-family: var(--mono); }
.bayes-flow-arrow { font-size: 1.125rem; color: var(--border2); }
.spss-table .annot { font-size: 0.6875rem; font-style: italic; color: var(--text3); font-family: 'IBM Plex Sans', sans-serif; }
.spss-table .annot strong { font-style: normal; }

/* ── QUIZ ── */
.quiz-wrap { background: var(--bg2); border: 1px solid var(--border); border-radius: 12px; padding: 20px; margin-top: 8px; }
.quiz-progress { display: flex; align-items: center; gap: 10px; margin-bottom: 16px; font-size: 0.6875rem; color: var(--text3); font-family: var(--mono); }
.quiz-prog-bar { flex: 1; height: 3px; background: var(--border); border-radius: 2px; overflow: hidden; }
.quiz-prog-fill { height: 100%; background: var(--accent); border-radius: 2px; transition: width .3s; }
.quiz-question { font-size: 0.875rem; font-weight: 600; color: var(--text); margin-bottom: 14px; line-height: 1.5; }
.quiz-options { display: flex; flex-direction: column; gap: 6px; }
.quiz-opt { display: flex; align-items: center; gap: 10px; padding: 10px 14px; border: 1px solid var(--border); border-radius: 8px; cursor: pointer; font-size: 0.8125rem; transition: all .15s; color: var(--text2); }
.quiz-opt:hover:not(.correct):not(.wrong):not(.disabled) { border-color: var(--border2); background: var(--bg3); color: var(--text); }
.quiz-opt.correct { border-color: var(--green); background: rgba(62,207,142,0.08); color: var(--green); }
.quiz-opt.wrong { border-color: var(--red); background: rgba(247,92,92,0.08); color: var(--red); }
.quiz-opt.disabled { opacity: 0.45; cursor: default; }
.quiz-opt-letter { width: 22px; height: 22px; border-radius: 50%; background: var(--bg3); border: 1px solid var(--border2); font-size: 0.6875rem; font-weight: 700; display: flex; align-items: center; justify-content: center; flex-shrink: 0; font-family: var(--mono); }
.quiz-explain { margin-top: 12px; padding: 10px 14px; background: rgba(79,142,247,0.06); border: 1px solid rgba(79,142,247,0.2); border-radius: 8px; font-size: 0.8125rem; color: var(--text2); line-height: 1.6; }
.quiz-correct-badge { color: var(--green); font-weight: 700; }
.quiz-wrong-badge { color: var(--red); font-weight: 700; }

.quiz-result { text-align: center; padding: 8px; }
.quiz-score { font-size: 3.25rem; font-weight: 700; font-family: var(--mono); margin-bottom: 6px; }
.quiz-score-label { font-size: 0.875rem; color: var(--text2); margin-bottom: 20px; }
.quiz-result-grid { display: flex; flex-direction: column; gap: 6px; text-align: left; }
.quiz-result-item { display: flex; align-items: center; gap: 8px; padding: 8px 12px; border-radius: 8px; font-size: 0.75rem; border: 1px solid var(--border); }
.quiz-result-item.correct { border-color: rgba(62,207,142,0.3); background: rgba(62,207,142,0.05); }
.quiz-result-item.wrong { border-color: rgba(247,92,92,0.3); background: rgba(247,92,92,0.05); }
.quiz-result-num { font-family: var(--mono); font-size: 0.6875rem; font-weight: 600; color: var(--text3); min-width: 24px; }
.quiz-result-text { color: var(--text2); flex: 1; }

/* Scrollbar */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border2); border-radius: 3px; }

/* ── MOBILE TOPBAR ── */
.topbar { display: none; }

/* ── SIDEBAR CLOSE BUTTON (ẩn trên desktop) ── */
.sb-close { display: none; }

/* ── SIDEBAR OVERLAY (mobile) ── */
.sb-overlay { display: none; }

/* ── MOBILE ── */
@media (max-width: 768px) {
  /* Sidebar: ẩn mặc định, slide in khi .open */
  .sidebar {
    position: fixed; top: 0; left: 0; height: 100vh; z-index: 200;
    transform: translateX(-100%); transition: transform .25s ease;
    box-shadow: 4px 0 24px rgba(0,0,0,0.5);
  }
  .sidebar.open { transform: translateX(0); }

  /* Nút đóng sidebar */
  .sb-close {
    display: flex; align-items: center; justify-content: center;
    background: none; border: none; color: var(--text3); font-size: 1rem;
    cursor: pointer; padding: 4px; border-radius: 4px; margin-left: auto;
  }
  .sb-close:hover { color: var(--text); background: var(--bg3); }

  /* Overlay tối khi sidebar mở */
  .sb-overlay {
    display: block; position: fixed; inset: 0; z-index: 199;
    background: rgba(0,0,0,0.5);
  }

  /* Topbar mobile */
  .topbar {
    display: flex; align-items: center; gap: 12px;
    padding: 12px 16px; background: var(--bg2);
    border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 10;
  }
  .hamburger {
    background: none; border: none; color: var(--text); font-size: 1.25rem;
    cursor: pointer; padding: 2px 6px; border-radius: 4px; line-height: 1;
  }
  .hamburger:hover { background: var(--bg3); }
  .topbar-title { font-size: 0.875rem; font-weight: 600; color: var(--accent); letter-spacing: 1px; flex: 1; }
  .topbar-progress { font-size: 0.75rem; color: var(--text3); font-family: var(--mono); }

  /* Nội dung */
  .lesson-hero, .content-area { padding: 20px 16px; }
  .metrics { grid-template-columns: repeat(2, 1fr); }
  .hero-title { font-size: 1.25rem; }
  .sb-header { display: flex; align-items: flex-start; }
}