/* Rùa Toán — phần riêng của web con, nạp SAU chung.css (chung.css chép nguyên từ cổng, không sửa).
   --mau  = màu ngách (xanh dương, cố định, trùng sổ gốc của cổng)
   --nhan = màu nhấn theo chuyên mục: luyện tập xanh dương · lớp 1 xanh lá · lớp 2 cam · lớp 3 tím · lớp 4 hồng · lớp 5 xanh ngọc */
[hidden] { display: none !important; }
:root { --nhan: var(--mau); }
.toan-nhan-nhat { background: color-mix(in srgb, var(--nhan) 10%, #fff); }

/* ── Dải đầu trang: gradient xanh + dấu toán bay lơ lửng ── */
.dau-ngach.toan-dau { position: relative; overflow: hidden; background:
  radial-gradient(700px 300px at 90% -10%, rgb(255 255 255 / .18), transparent 60%),
  linear-gradient(135deg, var(--mau), color-mix(in srgb, var(--mau) 55%, #1f2d5c)); }
.toan-dau .khung { position: relative; z-index: 1; }
.toan-ky-hieu { position: absolute; inset: 0; pointer-events: none; }
.toan-ky-hieu span { position: absolute; font-weight: 800; color: rgb(255 255 255 / .1); line-height: 1; animation: troi 7s ease-in-out infinite; }
.toan-ky-hieu span:nth-child(1) { left: 6%;  top: 18%; font-size: 4.5rem; }
.toan-ky-hieu span:nth-child(2) { left: 46%; top: 8%;  font-size: 3rem;   animation-delay: -2s; }
.toan-ky-hieu span:nth-child(3) { right: 8%; top: 22%; font-size: 5.5rem; animation-delay: -4s; color: rgb(252 211 77 / .22); }
.toan-ky-hieu span:nth-child(4) { left: 30%; bottom: 10%; font-size: 3.6rem; animation-delay: -1s; }
.toan-ky-hieu span:nth-child(5) { right: 30%; bottom: 18%; font-size: 3rem; animation-delay: -3s; color: rgb(163 214 28 / .22); }
.toan-ky-hieu span:nth-child(6) { right: 4%; bottom: 8%; font-size: 3.2rem; animation-delay: -5s; }
.toan-ky-hieu span:nth-child(7) { left: 64%; top: 52%; font-size: 2.4rem; animation-delay: -2.5s; }
.toan-ky-hieu span:nth-child(8) { left: 2%;  bottom: 4%; font-size: 2.8rem; animation-delay: -6s; color: rgb(252 211 77 / .2); }
@keyframes troi { 0%, 100% { transform: translateY(0) rotate(0); } 50% { transform: translateY(-10px) rotate(8deg); } }
@media (prefers-reduced-motion: reduce) { .toan-ky-hieu span { animation: none; } }

.toan-nhan-lop-dau { display: inline-block; font-size: .8rem; font-weight: 800; letter-spacing: .04em; text-transform: uppercase; background: var(--nhan); color: #fff; padding: 3px 12px; border-radius: 999px; margin-bottom: 10px; box-shadow: 0 2px 0 rgb(0 0 0 / .15); }

/* Trang chủ ngách: chữ + chú Rùa */
.toan-dau-chu .khung { padding-block: 40px 96px; }
.toan-dau-chu-luoi { display: grid; grid-template-columns: 1.3fr 1fr; gap: 24px; align-items: center; }
.toan-dau-chu h1 { font-size: clamp(2rem, 4.6vw, 3.2rem); }
.toan-nhan-vang { color: var(--vang); }
.toan-dau-chu .toan-linh-vat { justify-self: center; width: min(100%, 360px); filter: drop-shadow(0 18px 30px rgb(0 0 0 / .25)); animation: troi 6s ease-in-out infinite; }
.toan-nut-dau { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 24px; }
.nut.toan-nut-vang { --ngach-mau: var(--vang); color: var(--dam); box-shadow: 0 4px 0 #d4a514; }
.nut.toan-nut-trong { background: rgb(255 255 255 / .12); border: 2px solid rgb(255 255 255 / .7); box-shadow: none; }
@media (max-width: 760px) {
  .toan-dau-chu-luoi { grid-template-columns: 1fr; }
  .toan-dau-chu .toan-linh-vat { width: 200px; grid-row: 1; }
  .toan-dau-chu .khung { padding-block: 24px 72px; }
}

/* ── Khung bài tập ── */
.toan-bai-tap { background: var(--nen-the); border: 1px solid var(--vien); border-top: 6px solid var(--nhan); border-radius: 24px; box-shadow: var(--bong); padding: 24px; position: relative; }
@media (max-width: 560px) { .toan-bai-tap { padding: 14px; border-radius: 18px; } }

.toan-cai-dat { display: grid; gap: 10px; padding: 14px 16px; margin-bottom: 20px; border-radius: 16px; background: color-mix(in srgb, var(--nhan) 6%, #fff); }
.toan-hang-chon { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; }
.toan-nhan-chon { font-weight: 700; font-size: .9rem; color: var(--chu-phu); min-width: 82px; }
.toan-chip { font: inherit; font-weight: 700; font-size: .92rem; color: var(--dam); background: #fff; border: 2px solid var(--vien); border-radius: 999px; padding: 5px 14px; cursor: pointer; transition: border-color .15s, background .15s, transform .1s; }
.toan-chip:hover { border-color: var(--nhan); }
.toan-chip:active { transform: scale(.96); }
.toan-chip.toan-bat { background: var(--nhan); border-color: var(--nhan); color: #fff; box-shadow: 0 2px 0 color-mix(in srgb, var(--nhan) 60%, #000); }
.toan-o-pham-vi { font: inherit; font-weight: 700; width: 120px; padding: 5px 12px; border: 2px dashed var(--vien); border-radius: 999px; color: var(--dam); background: #fff; }
.toan-o-pham-vi.toan-bat, .toan-o-pham-vi:focus { border-style: solid; border-color: var(--nhan); outline: none; }

/* ── Phiếu câu hỏi ── */
.toan-phieu { list-style: none; margin: 0; padding: 0; display: grid; gap: 12px; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); }
.toan-cau { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; background: #fff; border: 2px solid var(--vien); border-bottom-width: 4px; border-radius: 18px; padding: 12px 14px; font-size: 1.4rem; font-weight: 800; color: var(--dam); transition: border-color .15s, transform .15s; }
.toan-cau:focus-within { border-color: var(--nhan); transform: translateY(-2px); }
.toan-cau .toan-so-cau { width: 32px; height: 32px; flex: none; border-radius: 10px; background: color-mix(in srgb, var(--nhan) 14%, #fff); color: var(--nhan); font-size: .85rem; display: grid; place-items: center; }
.toan-cau .toan-de { display: inline-flex; align-items: center; gap: 6px; flex-wrap: wrap; line-height: 1.6; }
.toan-cau .toan-de:has(br) { display: block; line-height: 1.9; }
.toan-cau .toan-dap-an { flex-basis: 100%; font-size: .9rem; font-weight: 700; }
.toan-cau .toan-dap-an:empty { display: none; }
.toan-cau.toan-dung { background: #f0fdf4; border-color: #4ade80; }
.toan-cau.toan-dung .toan-so-cau { background: #22c55e; color: #fff; }
.toan-cau.toan-dung .toan-dap-an { color: #15803d; }
.toan-cau.toan-sai { background: #fff1f2; border-color: #fb7185; animation: lac .35s; }
.toan-cau.toan-sai .toan-so-cau { background: #f43f5e; color: #fff; }
.toan-cau.toan-sai .toan-dap-an { color: #be123c; }
@keyframes lac { 25% { transform: translateX(-4px); } 75% { transform: translateX(4px); } }

input.toan-o { font: inherit; width: 3ch; min-width: 3ch; max-width: 12ch; text-align: center; padding: 2px 6px; border: 2px solid #c7d2e6; border-radius: 10px; background: #f8fafc; color: var(--dam); }
input.toan-o:focus { outline: none; border-color: var(--nhan); background: #fff; box-shadow: 0 0 0 3px color-mix(in srgb, var(--nhan) 22%, transparent); }
input.toan-o[readonly] { background: transparent; }

/* Phân số: tử trên, mẫu dưới */
.toan-ps { display: inline-flex; flex-direction: column; align-items: center; line-height: 1.1; vertical-align: middle; font-size: .9em; }
.toan-ps > span:first-child, .toan-o-ps > input:first-child { border-bottom: 2px solid currentColor; padding-bottom: 2px; margin-bottom: 2px; }
.toan-o-ps > input.toan-o { font-size: .95em; }

/* Chọn dấu > < = */
.toan-chon-dau { display: inline-flex; gap: 4px; }
.toan-chon-dau button { font: inherit; font-size: 1.1rem; width: 42px; height: 40px; border-radius: 10px; border: 2px solid #c7d2e6; border-bottom-width: 3px; background: #fff; color: var(--dam); cursor: pointer; }
.toan-chon-dau button:hover { border-color: var(--nhan); }
.toan-chon-dau button.toan-bat { background: var(--nhan); border-color: color-mix(in srgb, var(--nhan) 70%, #000); color: #fff; }
.toan-chon-dau.toan-khoa button { pointer-events: none; }

/* ── Nút + kết quả ── */
.toan-hanh-dong { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 22px; }
.toan-hanh-dong button { font: inherit; cursor: pointer; border: 0; }
.toan-bai-tap .nut, .toan-vung-choi .nut { --ngach-mau: var(--nhan); }   /* nút trong khung làm bài lấy màu nhấn của lớp */
.toan-nut-cham { --ngach-mau: #16a34a; font-size: 1.05rem; padding-inline: 32px; box-shadow: 0 4px 0 #15803d; }
.toan-nut-cham:active { transform: translateY(2px); box-shadow: 0 2px 0 #15803d; }
.toan-ket-qua { margin-top: 22px; display: grid; grid-template-columns: 120px 1fr; gap: 20px; align-items: center; background: linear-gradient(135deg, #fef9c3, var(--ma-nhat)); border: 2px solid var(--vang); border-radius: 22px; padding: 20px 24px; }
.toan-ket-qua img { width: 120px; animation: troi 3s ease-in-out infinite; }
.toan-ket-qua .toan-sao { font-size: 2.4rem; color: #f59e0b; letter-spacing: 4px; line-height: 1; }
.toan-ket-qua .toan-diem { font-size: 1.2rem; margin: 6px 0 2px; }
.toan-ket-qua .toan-diem strong { font-size: 2rem; color: var(--nhan); }
.toan-ket-qua p { margin: 0; color: var(--chu-phu); }
@media (max-width: 560px) { .toan-ket-qua { grid-template-columns: 1fr; text-align: center; } .toan-ket-qua img { width: 90px; margin: 0 auto; } }

/* ── Nội dung dưới bài tập ── */
.toan-meo { margin-top: 32px; display: grid; gap: 20px; grid-template-columns: 1.3fr 1fr; align-items: start; }
@media (max-width: 760px) { .toan-meo { grid-template-columns: 1fr; } }
.toan-meo .the { border-top: 4px solid var(--vang); }
.toan-meo .the h2 { font-size: 1.2rem; }
.toan-meo ul, .toan-huong-dan ol { margin: 0; padding-left: 1.2em; color: var(--chu-phu); }
.toan-meo li + li { margin-top: 6px; }

/* ── Thẻ ── */
.toan-the-lop { display: flex; flex-direction: column; gap: 6px; border-top: 5px solid var(--nhan); }
.toan-the-lop .toan-bt { width: 56px; height: 56px; border-radius: 18px; background: var(--nhan); color: #fff; display: grid; place-items: center; font-size: 1.6rem; font-weight: 800; margin-bottom: 8px; box-shadow: 0 4px 0 color-mix(in srgb, var(--nhan) 65%, #000); transform: rotate(-4deg); transition: transform .2s; }
a.toan-the-lop:hover .toan-bt { transform: rotate(4deg) scale(1.06); }
.toan-the-lop .toan-dem { font-size: .85rem; font-weight: 800; color: var(--nhan); margin-top: auto; padding-top: 8px; }
a.toan-the-lop:hover, a.toan-the-bai-tap:hover { border-color: var(--nhan); }
.toan-the-bai-tap { position: relative; padding-left: 26px; }
.toan-the-bai-tap::before { content: ''; position: absolute; left: 0; top: 18px; bottom: 18px; width: 6px; border-radius: 0 6px 6px 0; background: var(--nhan); }
.toan-the-bai-tap h3 { margin-bottom: 4px; }
.toan-nhan-lop { display: inline-block; font-size: .72rem; font-weight: 800; text-transform: uppercase; letter-spacing: .04em; color: var(--nhan); margin-bottom: 6px; }

/* ── In phiếu: chỉ in đề, ô trống thành gạch chân ── */
@media print {
  .toan-trang .thanh-tren, .toan-trang .chan-trang, .toan-trang .thanh-doi-mon, .toan-trang .muc-luc-ben, .toan-trang .muc-luc-gap, .toan-cai-dat, .toan-hanh-dong, .toan-ket-qua, .toan-meo, .toan-trang .lien-quan, .toan-dau .duong-dan, .toan-ky-hieu, .toan-nhan-lop-dau { display: none !important; }
  .dau-ngach.toan-dau { background: none; color: #000; }
  .toan-dau .khung { padding-block: 0 12px; }
  .toan-dau p { color: #333; }
  .toan-bai-tap { box-shadow: none; border: 0; margin: 0; padding: 0; }
  .toan-phieu { grid-template-columns: 1fr 1fr; gap: 6px 24px; }
  .toan-cau { background: none !important; border: 0; padding: 6px 0; font-size: 1.15rem; break-inside: avoid; transform: none; }
  .toan-cau .toan-so-cau { background: none; color: #000; }
  .toan-cau .toan-dap-an { display: none; }
  input.toan-o { border: 0; border-bottom: 2px dotted #000; border-radius: 0; width: 6ch !important; color: transparent; background: none; }
  .toan-chon-dau button { border: 1px solid #999; color: transparent; width: 28px; height: 28px; }
}

/* ═══ Chế độ chơi ═══ */
.toan-che-do { display: flex; gap: 6px; padding: 5px; margin-bottom: 16px; background: #eef2f9; border-radius: 16px; overflow-x: auto; scrollbar-width: none; }
.toan-che-do button { flex: 1 1 0; min-width: max-content; font: inherit; font-weight: 700; font-size: .95rem; color: var(--chu-phu); background: none; border: 0; border-radius: 12px; padding: 9px 14px; cursor: pointer; white-space: nowrap; }
.toan-che-do button:hover { color: var(--dam); }
.toan-che-do button[aria-selected='true'] { background: #fff; color: var(--nhan); box-shadow: 0 2px 6px rgb(31 45 92 / .12); }
.toan-dang-choi .toan-hang-so-cau { display: none; }

.toan-vung-choi { max-width: 560px; margin: 0 auto; }
.toan-choi-tren { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; font-weight: 800; color: var(--dam); margin-bottom: 12px; }
.toan-choi-tren .toan-mang { font-size: 1.4rem; letter-spacing: 2px; }
.toan-choi-tren .toan-diem-choi { background: var(--vang); padding: 2px 12px; border-radius: 999px; }
.toan-choi-tren .toan-chuoi { color: #ea580c; }
.toan-nut-tieng { margin-left: auto; font-size: 1.2rem; background: #fff; border: 2px solid var(--vien); border-radius: 12px; width: 42px; height: 38px; cursor: pointer; }

.toan-dong-ho { position: relative; height: 22px; background: #eef2f9; border-radius: 999px; overflow: hidden; margin-bottom: 14px; }
.toan-dong-ho .toan-thanh { height: 100%; width: 100%; background: linear-gradient(90deg, #22c55e, #84cc16); border-radius: 999px; }
.toan-dong-ho .toan-thanh.toan-gap { background: linear-gradient(90deg, #f43f5e, #f97316); }
.toan-dong-ho .toan-giay { position: absolute; inset: 0; display: grid; place-items: center; font-weight: 800; font-size: .85rem; color: var(--dam); }

.toan-the-choi { text-align: center; background: color-mix(in srgb, var(--nhan) 7%, #fff); border: 3px solid color-mix(in srgb, var(--nhan) 30%, #fff); border-bottom-width: 6px; border-radius: 26px; padding: 18px 16px 20px; transition: background .2s, border-color .2s; }
.toan-the-choi .toan-so-thu-tu { font-weight: 800; font-size: .85rem; color: var(--nhan); text-transform: uppercase; letter-spacing: .06em; }
.toan-de-choi { font-size: clamp(2rem, 8vw, 3rem); font-weight: 800; color: var(--dam); display: flex; justify-content: center; align-items: center; gap: 10px; flex-wrap: wrap; margin: 10px 0 6px; line-height: 1.4; }
.toan-de-choi.toan-co-xuong { display: block; }
.toan-de-choi input.toan-o { font-size: 1em; min-width: 2.2ch; border-width: 3px; border-radius: 14px; }
.toan-de-choi input.toan-o.toan-nhac { animation: lac .35s; border-color: #f97316; }
.toan-de-choi .toan-chon-dau button { width: 64px; height: 60px; font-size: 1.8rem; border-radius: 16px; }
.toan-phan-hoi { min-height: 1.8em; font-weight: 700; font-size: 1.05rem; }
.toan-phan-hoi .toan-khen { color: #15803d; font-size: 1.3rem; }
.toan-phan-hoi .toan-cong { display: inline-block; margin-left: 8px; color: #b45309; background: #fef3c7; padding: 0 10px; border-radius: 999px; animation: bay .9s ease-out; }
.toan-phan-hoi .toan-loi { color: #be123c; }
.toan-the-choi.toan-dung { background: #f0fdf4; border-color: #4ade80; animation: nay .35s; }
.toan-the-choi.toan-sai { background: #fff1f2; border-color: #fb7185; animation: lac .35s; }
@keyframes nay { 50% { transform: scale(1.03); } }
@keyframes bay { from { transform: translateY(8px); opacity: 0; } to { transform: none; opacity: 1; } }

.toan-ban-phim { display: grid; grid-template-columns: repeat(3, 1fr); gap: 8px; margin-top: 14px; }
.toan-ban-phim button { font: inherit; font-size: 1.6rem; font-weight: 800; color: var(--dam); background: #fff; border: 2px solid var(--vien); border-bottom-width: 5px; border-radius: 16px; padding: 10px 0; cursor: pointer; touch-action: manipulation; user-select: none; }
.toan-ban-phim button:active { transform: translateY(3px); border-bottom-width: 2px; }
.toan-ban-phim button.toan-an { visibility: hidden; }
.toan-ban-phim .toan-phim-rong { grid-column: 1 / -1; }
.toan-ban-phim .toan-phim-xong { background: #22c55e; border-color: #15803d; color: #fff; font-size: 1.3rem; }
.toan-choi-duoi { text-align: center; margin-top: 16px; }

.toan-man-cho { text-align: center; padding: 12px 8px 8px; }
.toan-man-cho h2 { font-size: 1.8rem; margin: 6px 0; }
.toan-man-cho p { color: var(--chu-phu); }
.toan-man-cho .toan-chon-giay { justify-content: center; margin: 14px 0; }
.toan-man-cho .toan-ky-luc { font-weight: 700; color: var(--dam); }
.toan-man-cho .toan-nut-bat-dau { --ngach-mau: #16a34a; font-size: 1.25rem; padding: 14px 44px; box-shadow: 0 5px 0 #15803d; cursor: pointer; border: 0; font-family: inherit; }
.toan-man-cho .toan-nut-dau { justify-content: center; }
.toan-man-cho .toan-nut-dau button { font: inherit; cursor: pointer; }
.toan-man-cho .toan-nut-dau button:not(.phu) { border: 0; }
.toan-dong-ho-to { font-size: 3.5rem; animation: troi 3s ease-in-out infinite; }
.toan-ket-thuc img { margin: 0 auto; width: 140px; animation: troi 3s ease-in-out infinite; }
.toan-so-lon { font-size: 3.6rem; font-weight: 800; color: var(--nhan); line-height: 1.1; }
.toan-so-lon small { font-size: 1.1rem; color: var(--chu-phu); }
.toan-thong-ke { list-style: none; padding: 0; margin: 12px 0 20px; display: flex; gap: 8px 18px; justify-content: center; flex-wrap: wrap; color: var(--chu-phu); }
.toan-thong-ke strong { color: var(--dam); }

/* Khối Thử thách ở trang chủ */
.toan-khoi-thu-thach { display: grid; grid-template-columns: 1fr 1.1fr; gap: 24px; align-items: center; padding: 28px; border-radius: 24px; color: #fff; background: radial-gradient(500px 220px at 100% 0%, rgb(255 255 255 / .16), transparent 60%), linear-gradient(135deg, #f97316, #db2777); box-shadow: var(--bong); }
.toan-khoi-thu-thach h2 { color: #fff; font-size: clamp(1.6rem, 3.4vw, 2.2rem); margin: 8px 0; }
.toan-khoi-thu-thach p { margin: 0; color: rgb(255 255 255 / .92); }
.toan-khoi-thu-thach .toan-nhan-lop-dau { --nhan: var(--dam); }
.toan-ktt-nut { display: flex; flex-wrap: wrap; gap: 10px; }
.toan-chip-tt { font-weight: 800; color: var(--dam); background: #fff; padding: 10px 16px; border-radius: 14px; text-decoration: none; box-shadow: 0 4px 0 rgb(0 0 0 / .18); border-left: 6px solid var(--nhan); transition: transform .12s; }
.toan-chip-tt:hover { transform: translateY(-2px); }
@media (max-width: 760px) { .toan-khoi-thu-thach { grid-template-columns: 1fr; padding: 20px; } }
@media print { .toan-che-do, .toan-vung-choi { display: none !important; } }
@media (max-width: 420px) { .toan-che-do { gap: 2px; padding: 4px; } .toan-che-do button { padding: 8px 6px; font-size: .82rem; } }
.toan-dang-choi .toan-cai-dat:not(:has(.toan-hang-chon:not(.toan-hang-so-cau))) { display: none; }

/* ═══ Chế độ tập trung: phần chơi phủ kín màn hình, xung quanh tối mờ ═══ */
body.toan-tap-trung { overflow: hidden; }
.toan-vung-choi:not([hidden]) { position: fixed; inset: 0; z-index: 100; max-width: none; margin: 0; overflow-y: auto; overscroll-behavior: contain;
  display: flex; padding: 16px; background: rgb(15 23 42 / .82); backdrop-filter: blur(8px); -webkit-backdrop-filter: blur(8px); animation: hien .2s ease-out; }
@keyframes hien { from { opacity: 0; } }
.toan-tt-khung { position: relative; width: 100%; max-width: 980px; margin: auto; background: radial-gradient(600px 260px at 100% 0%, color-mix(in srgb, var(--nhan) 10%, transparent), transparent 70%), #fff; border-radius: 30px; box-shadow: 0 30px 80px rgb(0 0 0 / .45); overflow: hidden; animation: phong .25s ease-out; }
@keyframes phong { from { transform: scale(.96); opacity: 0; } }
.toan-tt-thanh { display: flex; align-items: center; gap: 10px; padding: 12px 14px 12px 22px; background: var(--nhan); color: #fff; }
.toan-tt-ten { font-weight: 800; font-size: 1.05rem; flex: 1; min-width: 0; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.toan-tt-che-do { display: flex; gap: 4px; background: rgb(0 0 0 / .18); padding: 4px; border-radius: 14px; }
.toan-tt-che-do button { font: inherit; font-weight: 700; font-size: .88rem; color: rgb(255 255 255 / .85); background: none; border: 0; border-radius: 10px; padding: 6px 12px; cursor: pointer; white-space: nowrap; }
.toan-tt-che-do button[aria-selected='true'] { background: #fff; color: var(--nhan); }
.toan-tt-nut { flex: none; width: 40px; height: 40px; border-radius: 12px; border: 0; background: rgb(255 255 255 / .18); color: #fff; font-size: 1.15rem; font-weight: 800; cursor: pointer; }
.toan-tt-nut:hover { background: rgb(255 255 255 / .3); }
.toan-tt-noi-dung { padding: 20px 28px 28px; }

/* Bên trong khung: to hơn */
.toan-tap-trung .toan-choi-tren { font-size: 1.1rem; }
.toan-tap-trung .toan-de-choi { font-size: clamp(2.2rem, 6.5vw, 3.8rem); margin: 16px 0 10px; }
.toan-tap-trung .toan-the-choi { padding: 26px 18px 24px; display: flex; flex-direction: column; justify-content: center; min-height: 260px; }
.toan-tap-trung .toan-ban-phim button { font-size: 1.8rem; padding: 12px 0; }
.toan-choi-giua { display: grid; gap: 18px; align-items: stretch; }
@media (min-width: 900px) {
  .toan-choi-giua { grid-template-columns: 1.35fr 1fr; }
  .toan-choi-giua:has(.toan-ban-phim[hidden]) { grid-template-columns: 1fr; }
  .toan-tap-trung .toan-ban-phim { margin-top: 0; }
  .toan-tap-trung .toan-the-choi { min-height: 100%; }
}
.toan-tap-trung .toan-man-cho { padding: 28px 8px 16px; }

@media (max-width: 640px) {
  .toan-vung-choi:not([hidden]) { padding: 0; }
  .toan-tt-khung { border-radius: 0; min-height: 100%; margin: 0; display: flex; flex-direction: column; }
  .toan-tt-thanh { flex-wrap: wrap; padding: 10px 12px; gap: 8px; }
  .toan-tt-ten { flex-basis: calc(100% - 100px); order: 1; font-size: .95rem; }
  .toan-tt-nut { order: 2; width: 36px; height: 36px; }
  .toan-tt-che-do { order: 3; flex-basis: 100%; }
  .toan-tt-che-do button { flex: 1; }
  .toan-tt-noi-dung { padding: 14px 14px 20px; flex: 1; }
  .toan-tap-trung .toan-the-choi { min-height: 200px; }
  .toan-tap-trung .toan-ban-phim button { font-size: 1.6rem; padding: 10px 0; }
}
body.toan-tap-trung .toan-bai-tap { z-index: 1000; }
.toan-tap-trung .toan-de-choi.toan-de-dai { font-size: clamp(1.6rem, 4.6vw, 2.6rem); }

.toan-lien { white-space: nowrap; display: inline-flex; align-items: center; gap: 6px; }
@media (max-width: 640px) {
  .toan-tap-trung .toan-choi-tren { margin-bottom: 8px; }
  .toan-tap-trung .toan-the-choi { min-height: 0; padding: 14px 12px 12px; }
  .toan-tap-trung .toan-de-choi { margin: 8px 0 4px; }
  .toan-tap-trung .toan-ban-phim { gap: 6px; margin-top: 10px; }
  .toan-tap-trung .toan-ban-phim button { padding: 8px 0; font-size: 1.5rem; }
  .toan-tap-trung .toan-dong-ho { margin-bottom: 8px; }
  .toan-tap-trung .toan-choi-duoi { margin-top: 10px; }
}

/* ═══ Lời giải ═══ */
.toan-nut-giai { font: inherit; font-size: .82rem; font-weight: 700; color: var(--nhan); background: #fff; border: 1.5px solid currentColor; border-radius: 999px; padding: 1px 10px; margin-left: 6px; cursor: pointer; }
.toan-loi-giai { margin-top: 8px; }
.toan-loi-giai-noi { background: #fff; border: 1px dashed #c7d2e6; border-radius: 12px; padding: 10px 12px; color: var(--dam); font-weight: 500; font-size: .92rem; text-align: left; }
.toan-cac-buoc { margin: 0; padding-left: 1.2em; display: grid; gap: 4px; line-height: 1.55; }
.toan-cac-buoc b { color: var(--nhan); }
.toan-dat-tinh { float: right; margin: 0 0 6px 12px; padding: 6px 12px; background: #f8fafc; border-radius: 10px; font: 700 1.05rem/1.35 ui-monospace, 'Cascadia Mono', Consolas, monospace; color: var(--dam); }
.toan-loi-giai-noi::after { content: ''; display: block; clear: both; }
.toan-choi-giai { margin: 12px auto 0; max-width: 520px; }
.toan-tieu-de-giai { font-weight: 800; color: var(--nhan); margin-bottom: 6px; text-align: left; }
.toan-nut-tiep { margin-top: 12px; border: 0; cursor: pointer; font-family: inherit; }
.toan-tap-trung .toan-the-choi:has(.toan-choi-giai) { min-height: 0; }

/* Ví dụ có lời giải (tĩnh) */
.toan-vi-du-giai { margin-top: 32px; }
.toan-vi-du-giai h2 { font-size: 1.35rem; }
.toan-luoi-vi-du { display: grid; gap: 14px; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); }
.toan-vi-du { background: #fff; border: 1px solid var(--vien); border-left: 5px solid var(--nhan); border-radius: 16px; padding: 14px 16px; box-shadow: var(--bong); }
.toan-vd-de { font-size: 1.25rem; font-weight: 800; color: var(--dam); margin-bottom: 10px; display: flex; flex-wrap: wrap; align-items: center; gap: 8px; }
.toan-vd-so { font-size: .75rem; text-transform: uppercase; letter-spacing: .05em; background: color-mix(in srgb, var(--nhan) 12%, #fff); color: var(--nhan); padding: 2px 8px; border-radius: 999px; }
.toan-vd-bt { display: inline-flex; align-items: center; gap: 6px; flex-wrap: wrap; }
.toan-o-tinh { display: inline-grid; place-items: center; min-width: 1.8em; height: 1.5em; border: 2px dashed #c7d2e6; border-radius: 8px; color: var(--chu-phu); font-size: .85em; }
.toan-vd-dap { margin-top: 8px; font-weight: 700; color: var(--dam); }
.toan-vd-dap strong { color: #15803d; }
@media print { .toan-vi-du-giai, .toan-nut-giai, .toan-loi-giai { display: none !important; } }
.toan-cac-buoc li { line-height: 2.1; }
.toan-cac-buoc .toan-ps { font-size: .95em; margin: 0 3px; line-height: 1.15; vertical-align: middle; }

/* ═══ Toán có lời văn ═══ */
.toan-van { display: block; font-size: .72em; font-weight: 600; line-height: 1.55; margin-bottom: 4px; }
.toan-cau:has(.toan-van) { align-items: flex-start; }
.toan-cau .toan-de:has(.toan-van) { display: block; flex: 1; line-height: 1.8; }
.toan-tap-trung .toan-de-choi .toan-van { font-size: clamp(1.05rem, 2.6vw, 1.35rem); text-align: left; margin-bottom: 10px; }
.toan-vd-bt .toan-van { font-size: .8em; }
.toan-bai-giai { line-height: 1.6; }
.toan-bai-giai p { margin: 0; }
.toan-bg-tieu { font-weight: 800; text-decoration: underline; text-underline-offset: 3px; text-align: center; margin-bottom: 4px; }
.toan-bg-pt { padding-left: 2.2em; margin-bottom: 4px !important; }
.toan-bg-pt b { color: var(--nhan); }
.toan-bg-dap { padding-left: 1.2em; margin-top: 4px !important; font-weight: 700; }
.toan-van + br { display: none; }

/* ═══ Sách: mục lục chủ đề → bài, trang bài học ═══ */
.toan-ghi-sach { color: var(--chu-phu); margin: -6px 0 16px; }
.toan-tap-sach { font-size: 1.05rem; color: var(--nhan); text-transform: uppercase; letter-spacing: .06em; margin: 20px 0 10px; }
.toan-luoi-chu-de { display: grid; gap: 16px; grid-template-columns: repeat(auto-fill, minmax(320px, 1fr)); align-items: start; }
.toan-luoi-chu-de.toan-mot { grid-template-columns: 1fr; }
.toan-chu-de { border-top: 4px solid var(--nhan); }
.toan-chu-de h4 { margin: 0 0 8px; font-size: 1.05rem; line-height: 1.35; }
.toan-chu-de h4 span { display: block; font-size: .72rem; text-transform: uppercase; letter-spacing: .05em; color: var(--nhan); }
.toan-chu-de ol { list-style: none; margin: 0; padding: 0; display: grid; gap: 2px; }
.toan-chu-de li a, .toan-chu-de li.toan-sap-co { display: flex; gap: 10px; align-items: baseline; padding: 6px 8px; border-radius: 10px; text-decoration: none; color: var(--chu); font-weight: 600; font-size: .95rem; line-height: 1.4; }
.toan-chu-de li a:hover { background: color-mix(in srgb, var(--nhan) 8%, #fff); color: var(--nhan); }
.toan-chu-de li.toan-dang-xem a { background: var(--nhan); color: #fff; }
.toan-chu-de li.toan-dang-xem .toan-so-bai { color: rgb(255 255 255 / .85); }
.toan-so-bai { flex: none; min-width: 4.2em; font-size: .78rem; font-weight: 800; color: var(--nhan); }
.toan-chu-de li.toan-sap-co { color: var(--chu-phu); font-weight: 500; opacity: .75; }
.toan-chu-de li.toan-sap-co em { margin-left: auto; font-style: normal; font-size: .7rem; font-weight: 700; background: #eef2f9; padding: 1px 8px; border-radius: 999px; white-space: nowrap; }

.toan-chon-dang { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 14px; }
.toan-nut-dang { font: inherit; font-weight: 700; font-size: .9rem; color: var(--dam); background: #fff; border: 2px solid var(--vien); border-radius: 14px; padding: 6px 12px; cursor: pointer; text-align: left; line-height: 1.3; }
.toan-nut-dang span { display: block; font-size: .68rem; text-transform: uppercase; letter-spacing: .05em; color: var(--nhan); }
.toan-nut-dang:hover { border-color: var(--nhan); }
.toan-nut-dang.toan-bat { background: var(--nhan); border-color: var(--nhan); color: #fff; }
.toan-nut-dang.toan-bat span { color: rgb(255 255 255 / .85); }

.toan-lat-trang { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-top: 28px; }
.toan-lat { font-weight: 700; color: var(--dam); line-height: 1.4; }
.toan-lat span { display: block; font-size: .8rem; color: var(--nhan); margin-bottom: 2px; }
.toan-lat.toan-sau { text-align: right; }
@media (max-width: 560px) { .toan-lat-trang { grid-template-columns: 1fr; } .toan-lat.toan-sau { text-align: left; } .toan-luoi-chu-de { grid-template-columns: 1fr; } }
@media print { .toan-chon-dang, .toan-lat-trang { display: none !important; } }
.toan-do-vat { display: inline-flex; flex-direction: column; gap: 2px; font-size: 1.5em; line-height: 1.15; letter-spacing: 4px; margin-right: 8px; }
.toan-cau .toan-de:has(.toan-do-vat) { display: flex; flex-wrap: wrap; align-items: center; gap: 4px 10px; }
.toan-cau .toan-de:has(.toan-do-vat) .toan-van { margin: 0; flex-basis: 100%; }
.toan-de-choi .toan-do-vat { font-size: 1.2em; }

/* ═══ Lý thuyết ═══ */
.toan-ly-thuyet { margin-bottom: 28px; }
.toan-lt-khoi { background: #fff; border: 1px solid var(--vien); border-left: 6px solid var(--nhan); border-radius: 18px; padding: 16px 18px; margin-bottom: 14px; box-shadow: var(--bong); }
.toan-lt-khoi h3 { margin: 0 0 8px; font-size: 1.15rem; color: var(--dam); }
.toan-lt-than { display: flex; gap: 16px; align-items: center; flex-wrap: wrap; }
.toan-lt-than ul { flex: 1 1 260px; margin: 0; padding-left: 1.2em; display: grid; gap: 6px; }
.toan-lt-than b, .toan-lt-vd b { color: var(--nhan); }
.toan-lt-hinh { margin: 0; flex: 0 0 auto; }
.toan-lt-hinh .toan-hinh { width: 150px; max-width: 42vw; }
.toan-lt-hinh .toan-tia-so, .toan-lt-hinh .toan-thuoc { width: 300px; max-width: 80vw; }
.toan-lt-dem { font-size: 1.8rem; letter-spacing: 3px; }
.toan-lt-vd { margin-top: 10px; background: color-mix(in srgb, var(--nhan) 6%, #fff); border-radius: 12px; padding: 8px 12px; }
.toan-lt-vd ul { margin: 4px 0 0; padding-left: 1.2em; }

/* ═══ Hình trong bài tập ═══ */
.toan-hinh { display: block; height: auto; }
.toan-hinh-khung { display: block; flex-basis: 100%; }
.toan-hinh-khung .toan-hinh { width: 100%; max-width: 230px; margin: 4px 0; }
.toan-hinh-khung .toan-thuoc { max-width: 340px; }
.toan-hinh-khung .toan-dong-ho-hinh { max-width: 150px; }
.toan-de-choi .toan-hinh-khung .toan-hinh { max-width: 260px; margin: 0 auto; }
.toan-de-choi .toan-hinh-khung .toan-dong-ho-hinh { max-width: 190px; }
.cau .toan-de:has(.toan-hinh-khung), .cau .toan-de:has(.toan-lich), .cau .toan-de:has(.toan-bang-sl), .cau .toan-de:has(.toan-luoi-vi-tri) { display: flex; flex-wrap: wrap; align-items: center; gap: 6px 8px; flex: 1; }
.toan-day-hinh { display: flex; flex-wrap: wrap; align-items: center; gap: 2px; flex-basis: 100%; }
.toan-hinh-nho { width: 38px; }

/* Trắc nghiệm */
.toan-chon { flex-wrap: wrap; flex-basis: 100%; gap: 6px; }
.toan-chon button { width: auto; height: auto; min-height: 40px; padding: 6px 12px; font-size: .9rem; font-weight: 700; line-height: 1.25; }
.toan-chon button .toan-hinh { width: 46px; }
.toan-de-choi .toan-chon { justify-content: center; }
.toan-de-choi .toan-chon button { width: auto; height: auto; font-size: 1.05rem; padding: 10px 16px; }
.toan-chon-tinh { display: flex; flex-wrap: wrap; gap: 6px; flex-basis: 100%; }
.toan-chon-tinh > span { border: 1.5px dashed #c7d2e6; border-radius: 10px; padding: 2px 10px; font-size: .85rem; font-weight: 600; }
.toan-chon-tinh .toan-hinh { width: 40px; }

/* Lịch, bảng số liệu, tiền, vị trí, bóng */
.toan-lich, .toan-bang-sl { border-collapse: collapse; font-size: .85rem; font-weight: 700; background: #fff; flex-basis: 100%; max-width: 330px; }
.toan-lich caption { font-weight: 800; padding: 4px; color: var(--nhan); }
.toan-lich th, .toan-lich td { border: 1px solid #c7d2e6; width: 14.28%; text-align: center; padding: 3px 0; }
.toan-lich th:last-child, .toan-lich td:nth-child(7) { color: #dc2626; }
.toan-bang-sl th, .toan-bang-sl td { border: 1px solid #c7d2e6; padding: 4px 8px; text-align: center; }
.toan-bang-sl th { background: color-mix(in srgb, var(--nhan) 8%, #fff); }
.toan-bd-tranh td { text-align: left; font-size: 1.15rem; letter-spacing: 2px; }
.toan-vi-tien { display: flex; flex-wrap: wrap; gap: 6px; flex-basis: 100%; }
.toan-to-tien { display: inline-grid; place-items: center; min-width: 96px; padding: 6px 10px; border-radius: 8px; color: #fff; background: linear-gradient(135deg, var(--mt), color-mix(in srgb, var(--mt) 60%, #000)); border: 2px solid color-mix(in srgb, var(--mt) 50%, #000); line-height: 1.1; box-shadow: 0 2px 0 rgb(0 0 0 / .15); }
.toan-to-tien b { font-size: 1.05rem; } .toan-to-tien small { font-size: .65rem; font-weight: 600; opacity: .9; }
.toan-luoi-vi-tri { display: grid; grid-template-columns: repeat(3, 48px); grid-template-rows: repeat(3, 48px); gap: 3px; flex-basis: 100%; }
.toan-luoi-vi-tri span { display: grid; place-items: center; font-size: 1.9rem; background: #f8fafc; border-radius: 10px; }
.toan-hop-bong { display: inline-flex; flex-wrap: wrap; gap: 2px; padding: 8px 10px; border: 3px solid #a16207; border-top-width: 6px; border-radius: 0 0 14px 14px; background: #fef9c3; font-size: 1.4rem; max-width: 220px; flex-basis: auto; }
.toan-van + .toan-hinh-khung { margin-top: 2px; }
.toan-lt-dem { font-size: 1.5rem; letter-spacing: 2px; overflow-wrap: anywhere; word-break: break-all; max-width: 100%; }