/* ===== SAT 8020 (/sat8020) — design system NHÁI ĐÚNG ielts8020.com =====
   Màu, chữ, độ phẳng lấy nguyên từ ielts8020/style.css (navy #1C355F · hồng #ED0E57,
   Arial, góc gần vuông, kẻ mảnh 1px, không bóng loè) — học viên nhìn 2 web thấy cùng
   một hệ. Khu app này KHÔNG có footer, không form lead, không menu sản phẩm khác. */
:root {
  --navy:#1C355F; --navy-2:#274B85; --pink:#ED0E57; --pink-soft:#FFF0F5;
  --bg:#F7F9FC; --card:#FFFFFF; --line:#E5E7EB; --line-2:#D1D5DB;
  --muted:#6B7280; --text:#1F2937;
  --ok:#065F46; --okbg:#D1FAE5; --warn:#B45309; --warnbg:#FEF3E2;
  --err:#991B1B; --errbg:#FEE2E2;
  --radius:6px; --shadow:0 1px 2px rgba(16,24,40,.06);
}
* { box-sizing:border-box; margin:0; }
html { scroll-behavior:smooth; }
body { font-family:Arial,"Helvetica Neue",Helvetica,system-ui,-apple-system,sans-serif;
  background:var(--bg); color:var(--text); line-height:1.6; }
img { max-width:100%; }
a { color:var(--navy-2); }
.wrap { max-width:1080px; margin:0 auto; padding:0 20px; }
.muted { color:var(--muted); }
.hidden { display:none !important; }

/* ===== Header 2 tầng — y ielts8020 ===== */
.site-header { background:#fff; border-bottom:1px solid var(--line-2); position:sticky; top:0; z-index:200; }
.site-header .top-row { display:flex; align-items:center; gap:20px; height:58px; }
.site-logo { display:flex; align-items:center; gap:9px; text-decoration:none; flex:none; }
.site-logo img { height:36px; }
.site-logo span { font-weight:800; color:var(--navy); font-size:15px; letter-spacing:.2px; }
.header-cta { margin-left:auto; display:flex; gap:9px; align-items:center; }
.header-cta > .btn { padding:8px 15px; font-size:13.5px; }
.cta-stack { display:flex; flex-direction:column; align-items:stretch; gap:3px; min-width:0; }
.cta-stack .btn { padding:4px 13px; font-size:12.5px; line-height:1.4; border-radius:8px;
  max-width:250px; white-space:nowrap; overflow:hidden; text-overflow:ellipsis; }
.btn { display:inline-block; border:0; border-radius:4px; padding:10px 18px; font-size:14px;
  font-weight:700; cursor:pointer; text-decoration:none; text-align:center;
  -webkit-user-select:none; user-select:none; touch-action:manipulation; }
.btn-pink { background:var(--pink); color:#fff; }
.btn-pink:hover { background:#D00A4C; }
.btn-navy { background:var(--navy); color:#fff; }
.btn-navy:hover { background:#274B85; }
.btn-outline { background:#fff; color:var(--navy); border:1px solid var(--line-2); }
.btn-outline:hover { border-color:var(--navy); background:#F3F6FB; }
.btn-lg { padding:14px 28px; font-size:16px; }
.btn[disabled] { opacity:.5; cursor:not-allowed; }

/* Thanh tab: dải xám, tab đang chọn nổi trắng + gạch hồng đáy — y ielts8020 */
.tabbar { background:#EEF2F8; border-top:1px solid var(--line-2); border-bottom:1px solid var(--line-2); }
.main-nav { position:relative; display:flex; gap:0; align-items:stretch; justify-content:flex-start; }
.nav-item { position:static; display:flex; border-right:1px solid #DCE3ED; }
.nav-item:first-child { border-left:1px solid #DCE3ED; }
.main-nav a { position:relative; text-decoration:none; color:#374151; font-size:13.5px; font-weight:700;
  padding:12px 16px; border-bottom:3px solid transparent; border-radius:0;
  flex:0 0 auto; text-align:center; line-height:1.35; white-space:nowrap;
  display:flex; flex-direction:row; align-items:center; gap:7px; justify-content:center;
  transition:color .14s, background .14s, border-color .14s; }
.main-nav a:hover { color:var(--navy); background:#E3EAF4; }
.main-nav a.active { color:var(--navy); background:#fff; border-bottom-color:var(--pink);
  margin-bottom:-1px; padding-bottom:13px; }
.main-nav a.active:hover { background:#fff; }
.main-nav a .t-badge { background:#fff; color:var(--navy); border:1px solid var(--line-2);
  font-size:9.5px; font-weight:800; letter-spacing:.5px; border-radius:3px;
  padding:2px 5px; line-height:1.4; flex:none; }
.main-nav a.active .t-badge { border-color:var(--pink); color:var(--pink); }
/* Menu xổ ngang — y ielts8020 */
.nav-drop { position:absolute; top:100%; left:0; right:0; z-index:60;
  display:flex; flex-wrap:wrap; align-items:center; gap:8px; padding:12px 14px;
  background:#F4F7FB; border-bottom:1px solid var(--line-2);
  box-shadow:0 10px 24px rgba(16,24,40,.12);
  opacity:0; visibility:hidden; transform:translateY(-4px); transition:.14s ease; }
.nav-item.has-drop:hover .nav-drop, .nav-item.has-drop:focus-within .nav-drop {
  opacity:1; visibility:visible; transform:none; }
.main-nav .nav-drop a { flex:none; display:flex; align-items:center; justify-content:flex-start;
  gap:6px; text-align:left; white-space:nowrap; padding:9px 14px; font-size:13.5px;
  font-weight:600; color:var(--text); background:#fff; border:1px solid #DCE3ED;
  border-bottom:1px solid #DCE3ED; border-radius:4px; }
.main-nav .nav-drop a:hover { background:var(--navy); border-color:var(--navy); color:#fff; }

/* ===== Khung trang ===== */
.page { padding:28px 0 64px; }
.kicker { color:var(--pink); font-weight:800; font-size:13px; text-transform:uppercase; letter-spacing:1.2px; margin-bottom:6px; }
h1.page-title { color:var(--navy); font-size:clamp(26px,3.6vw,36px); line-height:1.2; letter-spacing:-.3px; }
.page-lead { color:var(--muted); font-size:16px; max-width:720px; margin-top:6px; }
h2.sec-title { color:var(--navy); font-size:clamp(20px,2.6vw,26px); line-height:1.25; margin:34px 0 12px; }
.grid { display:grid; gap:18px; }
.grid.c2 { grid-template-columns:repeat(auto-fit,minmax(320px,1fr)); }
.grid.c3 { grid-template-columns:repeat(auto-fit,minmax(250px,1fr)); }
.card { background:var(--card); border:1px solid var(--line); border-radius:var(--radius); padding:22px; box-shadow:var(--shadow); }
.card h3 { color:var(--navy); font-size:17px; margin-bottom:8px; }
.pill { display:inline-block; font-size:11px; font-weight:800; letter-spacing:.4px; border-radius:3px; padding:2px 7px; border:1px solid var(--line-2); color:var(--navy); background:#fff; }
.pill.pro { border-color:var(--pink); color:var(--pink); }
.pill.free { border-color:#0E9F6E; color:#0E9F6E; }
.pill.done { border-color:#0E9F6E; color:#065F46; background:var(--okbg); }

/* ===== Bố cục 2 cột: rail trái (3 mức khó) + nội dung ===== */
.layout { display:grid; grid-template-columns:230px 1fr; gap:26px; align-items:start; margin-top:22px; }
.rail { position:sticky; top:120px; background:#fff; border:1px solid var(--line); border-radius:var(--radius); overflow:hidden; }
.rail .rail-tieu-de { font-size:11px; font-weight:800; letter-spacing:.9px; text-transform:uppercase;
  color:var(--muted); padding:12px 16px 8px; }
.rail a { display:flex; align-items:center; justify-content:space-between; gap:8px; padding:11px 16px;
  font-size:14px; font-weight:600; color:var(--text); text-decoration:none; border-left:3px solid transparent; }
.rail a:hover { background:#F3F6FB; }
.rail a.on { color:var(--navy); background:var(--pink-soft); border-left-color:var(--pink); font-weight:800; }
.rail a .n { font-size:12px; color:var(--muted); font-weight:700; }
.rail .rail-chu-thich { font-size:12px; color:var(--muted); padding:10px 16px 14px; border-top:1px solid var(--line); line-height:1.5; }

/* Dải sub-tab 4 dạng nhỏ trong trang Verbal/Math */
.dom-tabs { display:flex; flex-wrap:wrap; gap:8px; margin:18px 0 4px; }
.dom-tabs a { text-decoration:none; font-size:13.5px; font-weight:700; color:var(--text);
  background:#fff; border:1px solid #DCE3ED; border-radius:4px; padding:9px 14px; }
.dom-tabs a.on { background:var(--navy); border-color:var(--navy); color:#fff; }
.dom-tabs a:hover:not(.on) { border-color:var(--navy); }

/* Thẻ đề lẻ */
.de-list { display:grid; gap:10px; margin-top:14px; }
.de-item { display:flex; align-items:center; gap:14px; background:#fff; border:1px solid var(--line);
  border-radius:var(--radius); padding:14px 18px; text-decoration:none; color:var(--text); }
.de-item:hover { border-color:var(--navy); }
.de-item .ma { flex:none; font-size:11px; font-weight:800; color:var(--muted); letter-spacing:.4px;
  background:#F3F6FB; border-radius:3px; padding:3px 7px; }
.de-item .ten { font-weight:700; color:var(--navy); font-size:14.5px; line-height:1.4; }
.de-item .meta { margin-left:auto; flex:none; display:flex; align-items:center; gap:10px;
  font-size:12.5px; color:var(--muted); white-space:nowrap; }
.de-item .diem { font-weight:800; color:var(--ok); }

/* Thẻ đề full / dự đoán */
.full-card { background:#fff; border:1px solid var(--line); border-radius:var(--radius); padding:20px; display:flex; flex-direction:column; gap:9px; }
.full-card h3 { color:var(--navy); font-size:16.5px; line-height:1.35; }
.full-card .chi-tiet { font-size:13px; color:var(--muted); line-height:1.55; }
/* Mô tả trọng tâm của đề dự đoán do người soạn viết, dài ngắn rất khác nhau —
   có thẻ 2 dòng, có thẻ 8 dòng, để nguyên thì cả lưới so le như răng cưa.
   Kẹp 4 dòng cho các thẻ cao bằng nhau; ai cần đọc đủ thì rê chuột (title). */
.full-card .chi-tiet.trong-tam { display:-webkit-box; -webkit-line-clamp:4;
  -webkit-box-orient:vertical; overflow:hidden; }
.full-card .hang-nut { margin-top:auto; display:flex; gap:8px; align-items:center; flex-wrap:wrap; }
.full-card .kq-cu { font-size:12.5px; color:var(--ok); font-weight:700; }

/* Hộp PRO — kiểu pro-box của luyenthi + bảng gói của ielts8020 */
.pro-box { background:#fff; border:2px solid var(--pink); border-radius:var(--radius); padding:24px; margin-top:26px; }
.pro-box h3 { color:var(--navy); font-size:19px; }
.goi-grid { display:grid; grid-template-columns:repeat(auto-fit,minmax(200px,1fr)); gap:14px; margin-top:16px; }
.goi { border:1px solid var(--line-2); border-radius:var(--radius); padding:18px; display:flex; flex-direction:column; gap:6px; background:#fff; }
.goi.hay { border-color:var(--pink); box-shadow:0 0 0 1px var(--pink); position:relative; }
.goi .nhan { font-size:12px; font-weight:800; letter-spacing:.5px; text-transform:uppercase; color:var(--muted); }
.goi.hay .nhan { color:var(--pink); }
.goi .gia { font-size:24px; font-weight:800; color:var(--navy); }
.goi .gia small { font-size:13px; color:var(--muted); font-weight:600; }
.goi .ngay { font-size:12.5px; color:var(--ok); font-weight:700; }
.goi .mo { font-size:13px; color:var(--muted); line-height:1.5; }
.goi .btn { margin-top:auto; }
.msg { border-radius:4px; padding:10px 14px; font-size:13.5px; margin-top:10px; }
.msg.err { background:var(--errbg); color:var(--err); }
.help { background:#F8FAFC; border:1px dashed var(--line-2); border-radius:4px; padding:12px 14px; font-size:13px; color:var(--muted); margin-top:12px; }

/* ===== Lộ trình của Tôi ===== */
.lt-hero { background:linear-gradient(135deg,#FFF0F5,#FDF6F9 60%,#fff); border:1px solid #F5D3DF;
  border-radius:var(--radius); padding:24px; margin-top:20px; display:flex; gap:20px; align-items:center; flex-wrap:wrap; }
.lt-hero .noi-dung { flex:1 1 380px; }
.lt-hero h2 { color:var(--navy); font-size:20px; margin-bottom:6px; }
.stat-grid { display:grid; grid-template-columns:repeat(auto-fit,minmax(150px,1fr)); gap:14px; margin-top:18px; }
.stat { background:#fff; border:1px solid var(--line); border-radius:var(--radius); padding:16px 18px; }
.stat .so { font-size:26px; font-weight:800; color:var(--navy); font-variant-numeric:tabular-nums; }
.stat .so small { font-size:13px; color:var(--muted); font-weight:600; }
.stat .ten { font-size:12.5px; color:var(--muted); margin-top:2px; }
/* Thanh Skills Insight: 8 dạng nhỏ, % đúng */
.si-grid { display:grid; grid-template-columns:1fr 1fr; gap:6px 36px; margin-top:14px; }
.si-cot h4 { color:var(--navy); font-size:14.5px; margin:10px 0 8px; }
.si-item { padding:7px 0; border-bottom:1px solid var(--line); }
.si-item .d { display:flex; justify-content:space-between; font-size:13px; margin-bottom:4px; }
.si-item .d b { color:var(--navy); font-weight:700; }
.si-item .d span { color:var(--muted); font-variant-numeric:tabular-nums; }
.si-bar { height:9px; background:#EEF2F8; border-radius:2px; overflow:hidden; display:flex; }
.si-bar i { display:block; height:100%; background:var(--navy); }
.si-bar i.thap { background:var(--pink); }
/* Lịch sử làm bài */
.ls-table { width:100%; border-collapse:collapse; font-size:13.5px; background:#fff; border:1px solid var(--line); }
.ls-table th { text-align:left; font-size:11.5px; letter-spacing:.5px; text-transform:uppercase; color:var(--muted); padding:10px 14px; border-bottom:1px solid var(--line-2); background:#F8FAFC; }
.ls-table td { padding:10px 14px; border-bottom:1px solid var(--line); }
.ls-table tr:last-child td { border-bottom:0; }

/* ===== Kết quả HV ===== */
.wins-grid { display:grid; grid-template-columns:repeat(auto-fit,minmax(240px,1fr)); gap:18px; margin-top:18px; }
.win-card { background:#fff; border:1px solid var(--line); border-radius:var(--radius); padding:22px; }
.win-top { display:flex; align-items:baseline; gap:8px; }
.win-label { font-size:11px; font-weight:800; letter-spacing:.8px; color:#fff; background:var(--navy); border-radius:3px; padding:2px 7px; }
.win-total { font-size:34px; font-weight:800; color:var(--navy); }
.win-max { color:var(--muted); font-size:14px; }
.win-subs { display:flex; gap:18px; margin:10px 0; }
.win-sub b { display:block; font-size:19px; color:var(--navy); }
.win-sub span { font-size:11.5px; color:var(--muted); }
.win-stars { color:#F59E0B; letter-spacing:2px; }
.win-name { font-weight:800; color:var(--navy); margin-top:6px; }
.win-course { font-size:12.5px; color:var(--muted); }
.win-quote { font-size:13px; color:var(--text); margin-top:8px; font-style:italic; }

/* =====================================================================
   PHÒNG THI — nhái màn Bluebook (Digital SAT). Nền trắng, thanh trên/dưới
   kẻ mảnh, chữ đen, không màu mè. Chỉ dùng trong thi.html / lam-bai.html.
   ===================================================================== */
body.exam { background:#fff; }
.bb-top { position:sticky; top:0; z-index:100; background:#fff; border-bottom:1px solid #E5E7EB;
  display:grid; grid-template-columns:1fr auto 1fr; align-items:center; padding:10px 22px; gap:10px; }
.bb-top .ten-de { font-size:14px; font-weight:700; color:#111827; justify-self:start; line-height:1.3; }
.bb-top .ten-de small { display:block; font-weight:400; color:#6B7280; font-size:12px; }
.bb-timer { justify-self:center; text-align:center; }
.bb-timer .t { font-size:20px; font-weight:800; color:#111827; font-variant-numeric:tabular-nums; letter-spacing:.5px; }
.bb-timer .t.sap-het { color:#B91C1C; }
.bb-timer button { background:none; border:1px solid #D1D5DB; border-radius:999px; font-size:11px; padding:2px 12px; cursor:pointer; color:#374151; }
.bb-top .cong-cu { justify-self:end; display:flex; gap:14px; align-items:center; }
.bb-top .cong-cu button, .bb-top .cong-cu a { background:none; border:0; cursor:pointer; color:#111827;
  font-size:12px; display:flex; flex-direction:column; align-items:center; gap:1px; text-decoration:none; }
.bb-top .cong-cu .ico { font-size:17px; line-height:1; }
.bb-stage { max-width:1240px; margin:0 auto; padding:26px 22px 90px; }
/* RW: đoạn văn trái — câu hỏi phải, kẻ giữa như Bluebook */
.bb-2cot { display:grid; grid-template-columns:1fr 1fr; gap:0; min-height:52vh; }
.bb-2cot .doan { padding:6px 34px 6px 6px; border-right:2px solid #E5E7EB; font-size:15.5px; line-height:1.75; color:#111827; }
.bb-2cot .hoi { padding:6px 6px 6px 34px; }
.bb-1cot { max-width:720px; margin:0 auto; }
.q-so-hang { display:flex; align-items:center; gap:10px; background:#F3F4F6; border-bottom:1px solid #D1D5DB; padding:6px 10px; margin-bottom:18px; }
.q-so { background:#111827; color:#fff; font-weight:800; font-size:14px; padding:2px 10px; }
.q-danh-dau { display:flex; align-items:center; gap:5px; font-size:12.5px; color:#374151; background:none; border:0; cursor:pointer; }
.q-danh-dau .co { font-size:15px; }
.q-danh-dau.on { color:#B91C1C; font-weight:700; }
.q-gach-btn { margin-left:auto; background:none; border:1px solid #9CA3AF; border-radius:3px; font-size:11px; font-weight:700; padding:1px 7px; cursor:pointer; color:#374151; text-decoration:line-through; }
.q-gach-btn.on { background:#111827; color:#fff; border-color:#111827; }
.q-stem { font-size:15.5px; line-height:1.7; color:#111827; }
.q-stem table { border-collapse:collapse; margin:14px auto; font-size:14px; }
.q-stem table th, .q-stem table td { border:1px solid #6B7280; padding:6px 12px; text-align:center; }
.q-stem table th { background:#F3F4F6; }
.q-fig { margin:14px auto; text-align:center; max-width:420px; }
.q-fig svg { width:100%; height:auto; }
.q-opts { list-style:none; padding:0; margin:18px 0 0; display:grid; gap:10px; }
.q-opt { position:relative; display:flex; align-items:flex-start; gap:12px; border:1px solid #6B7280;
  border-radius:6px; padding:11px 14px; cursor:pointer; font-size:15px; line-height:1.55; background:#fff; }
.q-opt:hover { background:#F9FAFB; }
.q-opt .chu { flex:none; width:26px; height:26px; border:1.5px solid #111827; border-radius:50%;
  display:flex; align-items:center; justify-content:center; font-weight:800; font-size:13px; }
.q-opt.chon { border:2px solid #2563EB; padding:10px 13px; background:#EFF6FF; }
.q-opt.chon .chu { background:#2563EB; border-color:#2563EB; color:#fff; }
.q-opt.gach { opacity:.45; }
.q-opt.gach .nd { text-decoration:line-through; }
.q-opt .gach-x { position:absolute; right:8px; top:8px; font-size:11px; border:1px solid #9CA3AF;
  border-radius:3px; padding:0 5px; background:#fff; cursor:pointer; display:none; }
.bb-stage.che-do-gach .q-opt .gach-x { display:block; }
/* chấm chữa (đề lẻ + xem lại): tô đúng/sai */
.q-opt.dung { border:2px solid #059669; background:#ECFDF5; }
.q-opt.dung .chu { background:#059669; border-color:#059669; color:#fff; }
.q-opt.sai { border:2px solid #DC2626; background:#FEF2F2; }
.q-opt.sai .chu { background:#DC2626; border-color:#DC2626; color:#fff; }
.q-spr input { font-size:18px; padding:9px 13px; border:1.5px solid #6B7280; border-radius:5px; width:190px; font-family:inherit; }
.q-spr .luat { font-size:12.5px; color:#6B7280; margin-top:8px; line-height:1.6; }
.q-giai { margin-top:18px; border:1px solid var(--line-2); border-left:4px solid var(--navy); background:#F8FAFC; border-radius:4px; padding:14px 16px; font-size:14px; line-height:1.7; }
.q-giai .bay { margin-top:8px; color:var(--warn); }
.q-giai .nhan { font-size:11px; font-weight:800; letter-spacing:.6px; text-transform:uppercase; color:var(--muted); display:block; margin-bottom:4px; }
/* Thanh dưới */
.bb-bottom { position:fixed; left:0; right:0; bottom:0; z-index:100; background:#fff; border-top:1px solid #E5E7EB;
  display:grid; grid-template-columns:1fr auto 1fr; align-items:center; padding:10px 22px; }
.bb-bottom .hv-ten { font-size:13.5px; font-weight:700; color:#111827; justify-self:start; }
.bb-qnav-btn { justify-self:center; background:#111827; color:#fff; border:0; border-radius:6px;
  font-size:13.5px; font-weight:700; padding:8px 16px; cursor:pointer; display:flex; align-items:center; gap:7px; }
.bb-bottom .di-chuyen { justify-self:end; display:flex; gap:9px; }
.bb-bottom .di-chuyen button { background:#2563EB; color:#fff; border:0; border-radius:999px;
  font-size:14px; font-weight:700; padding:9px 24px; cursor:pointer; }
.bb-bottom .di-chuyen button.lui { background:#fff; color:#2563EB; border:1px solid #2563EB; }
.bb-bottom .di-chuyen button[disabled] { opacity:.4; cursor:not-allowed; }
/* Bảng câu hỏi (question palette) nổi từ nút giữa */
.bb-palette { position:fixed; bottom:64px; left:50%; transform:translateX(-50%); z-index:120;
  background:#fff; border:1px solid #D1D5DB; border-radius:8px; box-shadow:0 12px 34px rgba(16,24,40,.22);
  padding:16px 18px; width:min(480px, 94vw); }
.bb-palette h4 { font-size:13.5px; color:#111827; text-align:center; margin-bottom:4px; }
.bb-palette .chu-thich { display:flex; justify-content:center; gap:16px; font-size:11.5px; color:#374151;
  border-bottom:1px solid #E5E7EB; padding-bottom:8px; margin-bottom:10px; }
.bb-palette .o-luoi { display:grid; grid-template-columns:repeat(auto-fill,minmax(38px,1fr)); gap:7px; }
.bb-palette .o { position:relative; border:1px dashed #6B7280; background:#fff; color:#2563EB;
  font-weight:700; font-size:13px; padding:7px 0; text-align:center; cursor:pointer; border-radius:3px; }
.bb-palette .o.da-tra-loi { background:#2563EB; border:1px solid #2563EB; color:#fff; }
.bb-palette .o.hien-tai::after { content:"📍"; position:absolute; top:-9px; right:-4px; font-size:11px; }
.bb-palette .o.danh-dau { outline:2px solid #B91C1C; outline-offset:1px; }
.bb-palette .dong { display:block; margin:12px auto 0; background:none; border:1px solid #2563EB;
  color:#2563EB; border-radius:999px; font-size:12.5px; font-weight:700; padding:5px 18px; cursor:pointer; }
/* Màn giữa module / nộp / kết quả */
.bb-nghi { max-width:640px; margin:60px auto; text-align:center; }
.bb-nghi h2 { color:#111827; font-size:24px; margin-bottom:10px; }
.bb-nghi p { color:#374151; margin-bottom:10px; }
.bb-nghi .dem { font-size:44px; font-weight:800; color:var(--navy); font-variant-numeric:tabular-nums; margin:16px 0; }
.kq-box { max-width:760px; margin:40px auto; }
.kq-tong { display:flex; gap:20px; align-items:center; justify-content:center; flex-wrap:wrap; margin:22px 0; }
.kq-o { background:#fff; border:1px solid var(--line); border-radius:var(--radius); padding:20px 30px; text-align:center; min-width:170px; }
.kq-o .so { font-size:38px; font-weight:800; color:var(--navy); font-variant-numeric:tabular-nums; }
.kq-o .ten { font-size:12.5px; color:var(--muted); }
.kq-o.tong-diem { border:2px solid var(--pink); }
.kq-o.tong-diem .so { color:var(--pink); }
/* Reference sheet (toán) */
.bb-ref { position:fixed; top:64px; right:18px; z-index:130; width:min(560px,92vw); max-height:74vh; overflow:auto;
  background:#fff; border:1px solid #D1D5DB; border-radius:8px; box-shadow:0 14px 40px rgba(16,24,40,.25); padding:18px 20px; }
.bb-ref h4 { font-size:14px; margin-bottom:10px; color:#111827; }
.bb-ref .luoi { display:grid; grid-template-columns:repeat(auto-fill,minmax(150px,1fr)); gap:12px; font-size:12.5px; text-align:center; }
.bb-ref figure { margin:0; }
.bb-ref .dong { display:block; margin:14px auto 0; background:none; border:1px solid #2563EB; color:#2563EB;
  border-radius:999px; font-size:12.5px; font-weight:700; padding:5px 18px; cursor:pointer; }
/* chú thích đúng/sai ở màn xem lại */
.xem-lai-nav { display:flex; flex-wrap:wrap; gap:6px; margin:14px 0; }
.xem-lai-nav button { border:1px solid var(--line-2); background:#fff; border-radius:3px; min-width:34px;
  padding:5px 0; font-size:12.5px; font-weight:700; cursor:pointer; color:var(--text); }
.xem-lai-nav button.dung { background:var(--okbg); color:var(--ok); border-color:#A7F3D0; }
.xem-lai-nav button.sai { background:var(--errbg); color:var(--err); border-color:#FECACA; }
.xem-lai-nav button.on { outline:2px solid var(--navy); }

/* ===== Responsive ===== */
@media (max-width:900px) {
  .layout { grid-template-columns:1fr; }
  .rail { position:static; display:flex; flex-wrap:wrap; }
  .rail .rail-tieu-de, .rail .rail-chu-thich { display:none; }
  .rail a { border-left:0; border-bottom:3px solid transparent; flex:1 1 auto; justify-content:center; }
  .rail a.on { border-bottom-color:var(--pink); }
  .bb-2cot { grid-template-columns:1fr; }
  .bb-2cot .doan { border-right:0; border-bottom:2px solid #E5E7EB; padding:6px 6px 20px; margin-bottom:18px; }
  .bb-2cot .hoi { padding:6px; }
  .si-grid { grid-template-columns:1fr; }
}
@media (max-width:760px) {
  .main-nav { overflow-x:auto; -webkit-overflow-scrolling:touch; }
  .nav-drop { display:none; }
  .header-cta > .btn.an-mobile { display:none; }
  .bb-top { padding:8px 12px; }
  .bb-top .ten-de small { display:none; }
  .bb-stage { padding:18px 14px 100px; }
  .bb-bottom { padding:8px 12px; }
  .bb-bottom .hv-ten { display:none; }
  .bb-bottom { grid-template-columns:auto 1fr; }
  .bb-bottom .di-chuyen { justify-self:end; }
}