/* ============================================================
   Bảng nhân, chia từ 2 đến 9 — Tiện ích học toán
   Phong cách: sáng, thân thiện học sinh, mỗi bảng một sắc màu
   ============================================================ */
:root {
  --bg:        #eef2fb;   /* nền xanh rất nhạt */
  --bg-2:      #e4e9f7;
  --surface:   #ffffff;
  --line:      #e3e8f2;
  --ink:       #1d2740;   /* navy đậm */
  --ink-2:     #5b6685;
  --ink-3:     #8a93ad;

  --primary:   #4f6bf6;   /* indigo tươi */
  --primary-d: #3a52d8;
  --primary-l: #eaf0ff;

  --ok:        #14a35a;
  --ok-bg:     #e3f8ec;
  --err:       #e5484d;
  --err-bg:    #fdecec;
  --warn:      #f59e0b;
  --gold:      #f2b705;

  --font: "Nunito", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;

  --r-sm: 10px;
  --r-md: 14px;
  --r-lg: 20px;
  --shadow-sm: 0 1px 2px rgba(29,39,64,.06), 0 2px 8px rgba(29,39,64,.05);
  --shadow-md: 0 6px 22px rgba(29,39,64,.10);
}

* { margin: 0; padding: 0; box-sizing: border-box; }

body {
  font-family: var(--font);
  color: var(--ink);
  background:
    radial-gradient(1200px 500px at 80% -10%, #f4ecff 0%, transparent 60%),
    radial-gradient(1000px 460px at -5% 0%, #e6f6ff 0%, transparent 55%),
    var(--bg);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

.page { max-width: 1080px; margin: 0 auto; padding: 16px 18px 56px; }

/* ---------- Thanh trên / nút quay lại ---------- */
.topbar { display: flex; margin-bottom: 14px; }
.back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font);
  font-size: 14.5px;
  font-weight: 700;
  color: var(--ink-2);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 8px 15px 8px 12px;
  cursor: pointer;
  box-shadow: var(--shadow-sm);
  transition: color .15s, background .15s, transform .05s;
}
.back:hover { color: var(--primary); background: #fff; }
.back:active { transform: scale(.97); }
.back:focus-visible { outline: none; box-shadow: 0 0 0 3px rgba(79,107,246,.3); }

/* ---------- Tiêu đề ---------- */
.hero { text-align: center; margin: 8px 0 22px; }
.hero__title {
  font-size: clamp(1.7rem, 4.4vw, 2.6rem);
  font-weight: 900;
  letter-spacing: -.02em;
  line-height: 1.1;
  background: linear-gradient(120deg, #3a52d8, #7c4ddb 55%, #d94f9c);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.hero__desc {
  max-width: 620px;
  margin: 10px auto 0;
  font-size: clamp(.95rem, 2.3vw, 1.05rem);
  font-weight: 500;
  color: var(--ink-2);
  line-height: 1.55;
}

/* ---------- Tabs ---------- */
.tabs {
  display: flex;
  gap: 8px;
  padding: 6px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 999px;
  box-shadow: var(--shadow-sm);
  overflow-x: auto;
  scrollbar-width: none;
  margin-bottom: 22px;
}
.tabs::-webkit-scrollbar { display: none; }
.tab {
  flex: 1 0 auto;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  white-space: nowrap;
  font-family: var(--font);
  font-size: 14.5px;
  font-weight: 800;
  color: var(--ink-2);
  background: transparent;
  border: none;
  border-radius: 999px;
  padding: 11px 18px;
  cursor: pointer;
  transition: color .18s, background .18s;
}
.tab__ico {
  display: grid;
  place-items: center;
  width: 22px; height: 22px;
  border-radius: 7px;
  background: var(--bg-2);
  color: var(--ink-2);
  font-size: 14px;
  font-weight: 900;
  transition: background .18s, color .18s;
}
.tab:hover { color: var(--ink); }
.tab.is-active { color: #fff; background: var(--primary); box-shadow: 0 4px 14px rgba(79,107,246,.4); }
.tab.is-active .tab__ico { background: rgba(255,255,255,.25); color: #fff; }
.tab:focus-visible { outline: none; box-shadow: 0 0 0 3px rgba(79,107,246,.35); }

/* ---------- Panel ---------- */
.panel { animation: fade .25s ease; }
.panel[hidden] { display: none; }
@keyframes fade { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }

/* ---------- Thẻ bảng cửu chương ---------- */
.cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 16px;
}
.card {
  --c: var(--primary);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform .18s, box-shadow .18s;
}
.card:hover { transform: translateY(-4px); box-shadow: var(--shadow-md); }
.card__head {
  padding: 12px 16px;
  font-size: 1.05rem;
  font-weight: 900;
  color: #fff;
  background: var(--c);
  letter-spacing: .01em;
}
.card__body { padding: 6px 16px 12px; }
.row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 7px 0;
  border-bottom: 1px solid var(--line);
  font-weight: 600;
  font-size: .96rem;
}
.row:last-child { border-bottom: none; }
.row__q { color: var(--ink-2); font-variant-numeric: tabular-nums; }
.row__eq { color: var(--ink-3); margin: 0 6px; }
.row__a {
  font-weight: 900;
  color: var(--c);
  font-variant-numeric: tabular-nums;
  min-width: 34px; text-align: right;
}

/* ---------- Nút chung ---------- */
.btn {
  font-family: var(--font);
  font-weight: 800;
  font-size: 15px;
  border: none;
  border-radius: var(--r-sm);
  cursor: pointer;
  transition: background .15s, transform .05s, box-shadow .15s, color .15s;
}
.btn--primary {
  background: var(--primary);
  color: #fff;
  padding: 12px 22px;
  box-shadow: 0 3px 10px rgba(79,107,246,.35);
}
.btn--primary:hover { background: var(--primary-d); }
.btn--primary:active { transform: translateY(1px); }
.btn--ghost {
  background: var(--surface);
  color: var(--ink-2);
  border: 1px solid var(--line);
  padding: 12px 22px;
}
.btn--ghost:hover { color: var(--ink); }
.btn--lg { width: 100%; padding: 15px; font-size: 16px; }
.btn:focus-visible { outline: none; box-shadow: 0 0 0 3px rgba(79,107,246,.35); }

/* ---------- Luyện tập (quiz) ---------- */
.quiz {
  max-width: 560px;
  margin: 0 auto;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-sm);
  padding: 26px 24px;
}
.quiz__heading { font-size: 1.15rem; font-weight: 900; text-align: center; margin-bottom: 20px; }
.quiz__row { margin-bottom: 20px; }
.quiz__label { display: block; font-size: 14px; font-weight: 800; color: var(--ink-2); margin-bottom: 9px; }

.seg { display: inline-flex; background: var(--bg); border-radius: var(--r-sm); padding: 4px; gap: 4px; }
.seg__btn {
  font-family: var(--font);
  font-weight: 800; font-size: 14px;
  color: var(--ink-2);
  background: transparent;
  border: none; border-radius: 8px;
  padding: 9px 18px; cursor: pointer;
  transition: background .15s, color .15s;
}
.seg__btn.is-on { background: #fff; color: var(--primary); box-shadow: var(--shadow-sm); }

.chips { display: flex; flex-wrap: wrap; gap: 8px; }
.chip {
  font-family: var(--font);
  font-weight: 800; font-size: 14px;
  color: var(--ink-2);
  background: var(--bg);
  border: 1.5px solid transparent;
  border-radius: 999px;
  padding: 8px 15px; cursor: pointer;
  transition: all .15s;
  font-variant-numeric: tabular-nums;
}
.chip:hover { border-color: var(--primary); color: var(--primary); }
.chip.is-on { background: var(--primary-l); border-color: var(--primary); color: var(--primary-d); }

.quiz__stats { display: flex; gap: 10px; margin-bottom: 18px; }
.stat {
  flex: 1;
  text-align: center;
  background: var(--bg);
  border-radius: var(--r-sm);
  padding: 10px 6px;
}
.stat__k { display: block; font-size: 12px; font-weight: 700; color: var(--ink-3); text-transform: uppercase; letter-spacing: .04em; }
.stat__v { display: block; font-size: 1.5rem; font-weight: 900; color: var(--ink); font-variant-numeric: tabular-nums; }

.quiz__question {
  text-align: center;
  font-size: clamp(2rem, 8vw, 3rem);
  font-weight: 900;
  color: var(--ink);
  padding: 18px 0 8px;
  font-variant-numeric: tabular-nums;
  letter-spacing: .01em;
}
.quiz__answer {
  width: 100%;
  font-family: var(--font);
  font-size: 1.5rem; font-weight: 800;
  text-align: center;
  color: var(--ink);
  background: var(--bg);
  border: 2px solid var(--line);
  border-radius: var(--r-md);
  padding: 14px;
  transition: border-color .15s, background .15s;
}
.quiz__answer:focus-visible { outline: none; border-color: var(--primary); background: #fff; box-shadow: 0 0 0 3px rgba(79,107,246,.18); }
.quiz__answer.is-ok { border-color: var(--ok); background: var(--ok-bg); }
.quiz__answer.is-err { border-color: var(--err); background: var(--err-bg); }

.quiz__feedback { text-align: center; font-weight: 800; font-size: 15px; min-height: 24px; padding: 10px 0; }
.quiz__feedback.ok { color: var(--ok); }
.quiz__feedback.err { color: var(--err); }
.quiz__actions { display: flex; gap: 10px; }
.quiz__actions .btn { flex: 1; }

/* ---------- Máy tính ---------- */
.calc {
  max-width: 460px;
  margin: 0 auto;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-sm);
  padding: 24px;
}
.calc__display {
  background: var(--ink);
  color: #fff;
  border-radius: var(--r-md);
  padding: 20px 22px;
  font-size: clamp(1.6rem, 7vw, 2.3rem);
  font-weight: 900;
  text-align: right;
  overflow-x: auto;
  white-space: nowrap;
  margin-bottom: 18px;
  font-variant-numeric: tabular-nums;
  min-height: 74px;
  display: flex; align-items: center; justify-content: flex-end;
}
.calc__inputs { display: flex; flex-direction: column; gap: 12px; margin-bottom: 18px; }
.calc__num {
  font-family: var(--font);
  font-size: 1.1rem; font-weight: 700;
  text-align: center;
  color: var(--ink);
  background: var(--bg);
  border: 2px solid var(--line);
  border-radius: var(--r-sm);
  padding: 12px;
}
.calc__num:focus-visible { outline: none; border-color: var(--primary); background: #fff; }
.calc__ops { display: grid; grid-template-columns: repeat(4, 1fr); gap: 8px; }
.opbtn {
  font-family: var(--font);
  font-size: 1.4rem; font-weight: 900;
  color: var(--ink-2);
  background: var(--bg);
  border: 2px solid transparent;
  border-radius: var(--r-sm);
  padding: 12px 0; cursor: pointer;
  transition: all .15s;
}
.opbtn:hover { color: var(--primary); }
.opbtn.is-on { background: var(--primary-l); border-color: var(--primary); color: var(--primary-d); }

/* ---------- Học số ---------- */
.tool {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-sm);
  padding: 22px;
  margin-bottom: 16px;
}
.tool__title { font-size: 1.1rem; font-weight: 900; margin-bottom: 14px; }
.tool__note { font-size: 13.5px; font-weight: 500; color: var(--ink-2); margin-bottom: 14px; }
.tool__row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
.tool__row--split .tool__input { flex: 1 1 130px; }
.tool__sep { font-weight: 800; color: var(--ink-2); font-size: 14px; }
.tool__input {
  flex: 1;
  min-width: 120px;
  font-family: var(--font);
  font-size: 1rem; font-weight: 700;
  color: var(--ink);
  background: var(--bg);
  border: 2px solid var(--line);
  border-radius: var(--r-sm);
  padding: 11px 14px;
}
.tool__input:focus-visible { outline: none; border-color: var(--primary); background: #fff; }
.tool__result {
  margin-top: 14px;
  padding: 14px 16px;
  border-radius: var(--r-md);
  font-weight: 700;
  font-size: .98rem;
  line-height: 1.55;
  background: var(--primary-l);
  border: 1px solid #d5e0ff;
  color: var(--ink);
}
.tool__result.ok  { background: var(--ok-bg);  border-color: #bff0d2; }
.tool__result.err { background: var(--err-bg); border-color: #f6c9c7; color: var(--err); }
.tags { display: flex; flex-wrap: wrap; gap: 7px; margin-top: 8px; }
.tag {
  font-size: 13px; font-weight: 800;
  padding: 4px 12px; border-radius: 999px;
  background: #fff; border: 1px solid var(--line);
}

/* Lưới số nguyên tố */
.primes {
  display: grid;
  grid-template-columns: repeat(10, 1fr);
  gap: 6px;
}
.prime {
  aspect-ratio: 1;
  display: grid;
  place-items: center;
  border-radius: 8px;
  font-weight: 800;
  font-size: clamp(.7rem, 2.4vw, .92rem);
  cursor: pointer;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink-2);
  font-variant-numeric: tabular-nums;
  transition: transform .12s;
}
.prime:hover { transform: scale(1.12); z-index: 1; }
.prime.is-prime { background: var(--primary); border-color: var(--primary); color: #fff; }
.prime.is-one   { background: var(--bg-2); color: var(--ink-3); }

/* Ghi nhớ nhanh */
.facts { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 12px; }
.fact {
  background: var(--bg);
  border-left: 4px solid var(--primary);
  border-radius: 0 var(--r-sm) var(--r-sm) 0;
  padding: 13px 15px;
}
.fact h3 { font-size: .98rem; font-weight: 900; margin-bottom: 5px; }
.fact p { font-size: .86rem; font-weight: 500; color: var(--ink-2); line-height: 1.5; }

/* ---------- Responsive ---------- */
@media (max-width: 560px) {
  .page { padding: 12px 12px 40px; }
  .tab { padding: 10px 14px; font-size: 13.5px; }
  .tab span:not(.tab__ico) { display: inline; }
  .cards { grid-template-columns: 1fr 1fr; gap: 12px; }
  .card__head { font-size: .95rem; padding: 10px 12px; }
  .card__body { padding: 4px 12px 10px; }
  .row { font-size: .85rem; padding: 6px 0; }
  .quiz, .calc, .tool { padding: 18px 16px; }
  .tool__row--split { flex-direction: column; align-items: stretch; }
  .tool__row--split .tool__sep { text-align: center; }
  .primes { grid-template-columns: repeat(10, 1fr); gap: 4px; }
  .facts { grid-template-columns: 1fr; }
}

@media (max-width: 380px) {
  .cards { grid-template-columns: 1fr; }
  .tab__ico { display: none; }
}

@media (prefers-reduced-motion: reduce) {
  .panel, .card, .prime, .btn, .back { transition: none; animation: none; }
}