body{margin:0}[hidden]{display:none!important}img{max-width:100%}
/* Layout: trang vở ô ly — thanh tab trên cùng, nội dung một cột rộng 1080px; bài học = danh sách chương bên trái + nội dung bên phải */
:root{
  /* Bảng màu theo đề xuất của Gemini (19/10/2026): giấy vở ấm, mực tím, bút đỏ */
  --paper:#faf9f5; --grid:#e2e8f0; --card:#ffffff; --line:#cbd5e1;
  --ink:#1e1b4b; --ink-soft:#64748b;
  --tim:#6d28d9; --tim-nhat:#f3e8ff;   /* mực tím học trò */
  --do:#dc2626; --do-nhat:#fee2e2;     /* bút đỏ cô giáo */
  --xanh:#16a34a; --xanh-nhat:#dcfce7;
  --vang:#d97706; --vang-nhat:#fef3c7;
  --f-display:"Nunito","Be Vietnam Pro",system-ui,sans-serif;
  --f-body:"Be Vietnam Pro",system-ui,-apple-system,"Segoe UI",sans-serif;
  --r:12px;
  /* Nền trang: mảng màu pastel + họa tiết học trò (img/nen-sang.svg) */
  --nen-mau:radial-gradient(ellipse 60% 50% at 0% 0%,#ede9fe 0,transparent 70%),radial-gradient(ellipse 50% 45% at 100% 10%,#fce7f3 0,transparent 70%),radial-gradient(ellipse 55% 50% at 100% 100%,#dcfce7 0,transparent 70%),radial-gradient(ellipse 55% 50% at 0% 100%,#fef3c7 0,transparent 70%);
  --nen-hoa:url("../img/nen-sang.svg");
}
@media (prefers-color-scheme: dark){:root:not([data-theme="light"]){
  --paper:#0f172a; --grid:#1e293b; --card:#1e293b; --line:#334155;
  --ink:#f8fafc; --ink-soft:#94a3b8;
  --tim:#a78bfa; --tim-nhat:#2e1065;
  --do:#f87171; --do-nhat:#450a0a;
  --xanh:#4ade80; --xanh-nhat:#052e16;
  --vang:#fbbf24; --vang-nhat:#451a03;
  --nen-mau:radial-gradient(ellipse 60% 50% at 0% 0%,rgba(124,58,237,.30) 0,transparent 70%),radial-gradient(ellipse 50% 45% at 100% 10%,rgba(219,39,119,.18) 0,transparent 70%),radial-gradient(ellipse 55% 50% at 100% 100%,rgba(14,165,233,.20) 0,transparent 70%),radial-gradient(ellipse 55% 50% at 0% 100%,rgba(79,70,229,.22) 0,transparent 70%);
  --nen-hoa:url("../img/nen-toi.svg");
  color-scheme:dark}}
:root[data-theme="dark"]{
  --paper:#0f172a; --grid:#1e293b; --card:#1e293b; --line:#334155;
  --ink:#f8fafc; --ink-soft:#94a3b8;
  --tim:#a78bfa; --tim-nhat:#2e1065;
  --do:#f87171; --do-nhat:#450a0a;
  --xanh:#4ade80; --xanh-nhat:#052e16;
  --vang:#fbbf24; --vang-nhat:#451a03;
  --nen-mau:radial-gradient(ellipse 60% 50% at 0% 0%,rgba(124,58,237,.30) 0,transparent 70%),radial-gradient(ellipse 50% 45% at 100% 10%,rgba(219,39,119,.18) 0,transparent 70%),radial-gradient(ellipse 55% 50% at 100% 100%,rgba(14,165,233,.20) 0,transparent 70%),radial-gradient(ellipse 55% 50% at 0% 100%,rgba(79,70,229,.22) 0,transparent 70%);
  --nen-hoa:url("../img/nen-toi.svg");
  color-scheme:dark}

*{box-sizing:border-box}
body{background:var(--paper);color:var(--ink);font-family:var(--f-body);font-size:16px;line-height:1.6;
  background-image:var(--nen-hoa),var(--nen-mau);background-size:320px 320px,100% 100%,100% 100%,100% 100%,100% 100%;background-repeat:repeat,no-repeat,no-repeat,no-repeat,no-repeat;background-attachment:fixed;min-height:100vh}
h1,h2,h3{font-family:var(--f-display);line-height:1.2;text-wrap:balance;margin:0}
button,input,select{font:inherit;color:inherit}
:focus-visible{outline:3px solid var(--tim);outline-offset:2px;border-radius:6px}
.wrap{max-width:1080px;margin:0 auto;padding-left:max(16px,env(safe-area-inset-left,0px));padding-right:max(16px,env(safe-area-inset-right,0px))}

/* Thanh trên */
.top{position:sticky;top:env(safe-area-inset-top,0px);z-index:10;background:color-mix(in srgb,var(--paper) 92%,transparent);backdrop-filter:blur(8px);border-bottom:1px solid var(--line)}
.top .wrap{display:flex;flex-wrap:wrap;align-items:center;gap:10px 18px;padding-block:10px}
.brand{display:flex;align-items:baseline;gap:8px;margin-right:auto}
.brand b{font-family:var(--f-display);font-size:1.55rem;font-weight:800;color:var(--tim);letter-spacing:-.01em}
.brand span{font-size:.8rem;color:var(--ink-soft)}
.tabs{display:flex;gap:4px;flex-wrap:wrap}
.tabs a{text-decoration:none;color:var(--ink-soft);font-weight:600;padding:6px 12px;border-radius:999px;font-size:.95rem}
.tabs a[aria-current="page"]{background:var(--tim);color:var(--card)}
.tabs a:hover:not([aria-current="page"]){background:var(--tim-nhat);color:var(--tim)}
.ten{display:flex;align-items:center;gap:6px;font-size:.85rem;color:var(--ink-soft)}
.ten input{width:8.5em;padding:4px 10px;border:1px solid var(--line);border-radius:999px;background:var(--card)}

main{padding-block:24px 64px}
section[data-view]{display:flex;flex-direction:column;gap:20px}
.lead{color:var(--ink-soft);max-width:65ch;margin:0}
.eyebrow{font-size:.75rem;letter-spacing:.08em;text-transform:uppercase;color:var(--ink-soft);font-weight:600}

/* Bài học */
.hoc{display:grid;grid-template-columns:270px 1fr;gap:24px;align-items:start}
.dsc{display:flex;flex-direction:column;gap:14px;position:sticky;top:calc(env(safe-area-inset-top,0px) + 78px)}
.dsc h3{font-size:.8rem;font-family:var(--f-body);letter-spacing:.08em;text-transform:uppercase;color:var(--ink-soft);margin-bottom:4px}
.dsc ul{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:2px}
.dsc button{width:100%;text-align:left;display:flex;gap:10px;align-items:baseline;background:none;border:0;padding:7px 10px;border-radius:8px;cursor:pointer;color:var(--ink)}
.dsc button .so{font-family:var(--f-display);font-weight:700;color:var(--tim);min-width:1.6em}
.dsc button:hover{background:var(--tim-nhat)}
.dsc button[aria-pressed="true"]{background:var(--card);box-shadow:0 0 0 1px var(--line);font-weight:600}
.dsc select{display:none;width:100%;padding:10px;border:1px solid var(--line);border-radius:10px;background:var(--card)}
.baihoc{background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:28px clamp(18px,4vw,40px);min-width:0}
.baihoc h3{font-size:1.25rem;color:var(--tim);margin-top:26px;margin-bottom:6px}
.baihoc p,.baihoc li{max-width:68ch}
.baihoc ul,.baihoc ol{padding-left:1.3em}
.rule{background:var(--tim-nhat);border-radius:10px;padding:12px 16px;margin:10px 0;max-width:68ch}
.rule b{color:var(--tim)}
.vd{border-left:3px solid var(--vang);background:var(--vang-nhat);border-radius:0 10px 10px 0;padding:12px 16px;margin:12px 0;max-width:68ch}
.vd .eyebrow{color:var(--vang)}
.vd ol{margin:6px 0 0}
.hinh{display:flex;justify-content:center;margin:8px 0;overflow-x:auto}
.hinh svg{max-width:100%;height:auto}
.hinh svg .net{stroke:var(--ink);stroke-width:2;fill:none}
.hinh svg .net2{stroke:var(--tim);stroke-width:2.5;fill:none}
.hinh svg .dash{stroke:var(--ink-soft);stroke-width:1.5;stroke-dasharray:5 4;fill:none}
.hinh svg text{fill:var(--ink);font-family:var(--f-body);font-size:14px}
.hinh svg .lbl{fill:var(--tim);font-weight:700}
.hinh svg .dot{fill:var(--do)}

/* Toán */
.fr{display:inline-flex;flex-direction:column;vertical-align:middle;text-align:center;font-size:.9em;line-height:1.15;margin:0 .12em}
.fr>span:first-child{border-bottom:1.5px solid currentColor;padding:0 .2em}
.fr>span:last-child{padding:0 .2em}
.rad{border-top:1.5px solid currentColor;padding:0 .12em 0 .08em}
sup{font-size:.7em;line-height:0}

/* Nút */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:8px;padding:10px 20px;border-radius:999px;border:0;background:var(--tim);color:var(--card);font-weight:700;cursor:pointer;font-size:1rem}
.btn:hover{filter:brightness(1.08)}
.btn.phu{background:transparent;color:var(--tim);box-shadow:inset 0 0 0 2px var(--tim)}
.btn:disabled{opacity:.45;cursor:not-allowed}
.hang{display:flex;flex-wrap:wrap;gap:10px;align-items:center}

/* Luyện tập */
.chon{display:grid;grid-template-columns:repeat(auto-fill,minmax(220px,1fr));gap:10px}
.chip{display:flex;flex-direction:column;gap:2px;text-align:left;padding:12px 14px;border-radius:10px;border:1px solid var(--line);background:var(--card);cursor:pointer;min-width:0}
.chip .so{font-family:var(--f-display);font-weight:700;color:var(--tim);font-size:.85rem}
.chip .t{font-weight:600;line-height:1.3}
.chip .kq{font-size:.8rem;color:var(--ink-soft)}
.chip[aria-pressed="true"]{border-color:var(--tim);box-shadow:0 0 0 2px var(--tim)}
.chip.tron{background:var(--tim-nhat)}
.cauhoi{background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:24px clamp(18px,4vw,36px);display:flex;flex-direction:column;gap:18px;max-width:760px;width:100%;margin:0 auto}
.tien{display:flex;gap:5px}
.tien i{flex:1;height:6px;border-radius:3px;background:var(--line)}
.tien i.dung{background:var(--xanh)} .tien i.sai{background:var(--do)} .tien i.dang{background:var(--tim)}
.de{font-size:1.22rem;line-height:1.75}
.de table{border-collapse:collapse;font-size:1rem;margin-top:8px}
.de td,.de th{border:1px solid var(--line);padding:4px 12px;text-align:center;font-variant-numeric:tabular-nums}
.de th{background:var(--tim-nhat);font-weight:600}
.bang{overflow-x:auto}
.nhap{display:flex;flex-wrap:wrap;gap:10px;align-items:center}
.nhap input{flex:1 1 180px;min-width:0;font-size:1.25rem;padding:10px 14px;border-radius:10px;border:2px solid var(--line);background:var(--paper);font-variant-numeric:tabular-nums}
.nhap input:focus{border-color:var(--tim);outline:none}
.goiy{font-size:.85rem;color:var(--ink-soft);margin:0}
.lc{display:grid;grid-template-columns:repeat(auto-fit,minmax(160px,1fr));gap:10px}
.lc button{padding:12px 14px;border-radius:10px;border:2px solid var(--line);background:var(--paper);cursor:pointer;text-align:left;font-size:1.05rem;display:flex;gap:10px;align-items:center}
.lc button .k{font-family:var(--f-display);font-weight:700;color:var(--tim);min-width:1.2em}
.lc button:hover:not(:disabled){border-color:var(--tim)}
.lc button.chon-dung{border-color:var(--xanh);background:var(--xanh-nhat)}
.lc button.chon-sai{border-color:var(--do);background:var(--do-nhat)}
.lc button:disabled{cursor:default}
.phan{border-radius:10px;padding:12px 16px;display:flex;flex-direction:column;gap:4px}
.phan.dung{background:var(--xanh-nhat)} .phan.sai{background:var(--do-nhat)} .phan.loi{background:var(--vang-nhat)}
.phan strong{font-family:var(--f-display);font-size:1.15rem}
.phan.dung strong{color:var(--xanh)} .phan.sai strong{color:var(--do)} .phan.loi strong{color:var(--vang)}

/* Kết quả — lời phê */
.ketqua{display:grid;grid-template-columns:auto 1fr;gap:24px;align-items:center;background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:24px clamp(18px,4vw,36px);max-width:760px;width:100%;margin:0 auto}
.diem{width:132px;height:132px;border:4px solid var(--do);border-radius:50%;display:flex;flex-direction:column;align-items:center;justify-content:center;color:var(--do);transform:rotate(-8deg)}
.diem b{font-family:var(--f-display);font-size:3.6rem;line-height:1}
.diem span{font-size:.8rem;font-weight:600;letter-spacing:.05em}
.loiphe{display:flex;flex-direction:column;gap:6px;min-width:0}
.loiphe .eyebrow{color:var(--do)}
.loiphe p{margin:0;font-size:1.15rem;color:var(--do);font-style:italic}
.xemlai{max-width:760px;width:100%;margin:0 auto;display:flex;flex-direction:column;gap:10px}
.xemlai details{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:10px 16px}
.xemlai summary{cursor:pointer;font-weight:600}
.xemlai .loigiai{margin-top:8px;color:var(--ink-soft)}

/* Trò chơi */
.game{background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:28px clamp(18px,4vw,40px);max-width:640px;width:100%;margin:0 auto;display:flex;flex-direction:column;gap:18px;align-items:stretch;text-align:center}
.game .so-lieu{display:flex;justify-content:space-between;gap:12px;font-variant-numeric:tabular-nums}
.game .so-lieu div{display:flex;flex-direction:column}
.game .so-lieu b{font-family:var(--f-display);font-size:2rem;line-height:1.1;color:var(--tim)}
.game .so-lieu .gio b{color:var(--do)}
.dong-ho{height:8px;border-radius:4px;background:var(--line);overflow:hidden}
.dong-ho i{display:block;height:100%;background:var(--do);transition:width .1s linear}
.phep{font-family:var(--f-display);font-size:clamp(2.2rem,8vw,3.4rem);font-weight:700;letter-spacing:.01em;font-variant-numeric:tabular-nums}
.game input{font-size:1.8rem;text-align:center;padding:10px;border-radius:12px;border:2px solid var(--line);background:var(--paper);width:100%;font-variant-numeric:tabular-nums}
.game input:focus{border-color:var(--tim);outline:none}
.game input.lac{animation:lac .3s}
@keyframes lac{25%{transform:translateX(-6px)}75%{transform:translateX(6px)}}
.game .chuoi{color:var(--xanh);font-weight:700;min-height:1.6em}

/* Tiến độ */
.the{display:grid;grid-template-columns:repeat(4,1fr);gap:12px}
.the div{background:var(--card);border:1px solid var(--line);border-radius:10px;padding:14px 16px;display:flex;flex-direction:column;gap:2px;min-width:0}
.the b{font-family:var(--f-display);font-size:1.9rem;line-height:1.15;color:var(--tim);font-variant-numeric:tabular-nums}
.the .nho{font-size:.8rem;color:var(--ink-soft)}
.the .on b{color:var(--do);font-size:1.2rem;font-family:var(--f-body);line-height:1.3}
.khoi{background:var(--card);border:1px solid var(--line);border-radius:var(--r);padding:20px clamp(16px,3vw,28px);display:flex;flex-direction:column;gap:12px;min-width:0}
.khoi h2{font-size:1.3rem}
.thanh{display:grid;grid-template-columns:minmax(0,15em) 1fr 4.5em;gap:10px;align-items:center;font-size:.92rem}
.thanh .ten-c{overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.thanh .ray{height:12px;border-radius:6px;background:var(--line);overflow:hidden}
.thanh .ray i{display:block;height:100%;border-radius:6px}
.thanh .pt{text-align:right;font-variant-numeric:tabular-nums;color:var(--ink-soft)}
.lich{width:100%;border-collapse:collapse;font-size:.92rem}
.lich th{text-align:left;font-weight:600;color:var(--ink-soft);font-size:.78rem;letter-spacing:.06em;text-transform:uppercase;padding:6px 8px;border-bottom:1px solid var(--line)}
.lich td{padding:8px;border-bottom:1px solid var(--line);vertical-align:top;font-variant-numeric:tabular-nums}
.lich .d{font-family:var(--f-display);font-weight:700;font-size:1.1rem}
.lich details summary{cursor:pointer;color:var(--tim);font-size:.85rem}
.lich details div{color:var(--ink-soft);font-size:.85rem;margin-top:4px}
.trong{color:var(--ink-soft);text-align:center;padding:24px}
.luu{font-size:.82rem;color:var(--ink-soft)}

/* Hình minh họa */
.art .a1{fill:var(--c)} .art .a2{fill:color-mix(in srgb,var(--c) 30%,var(--card))} .art .a3{fill:var(--card)}
.art .a4{fill:color-mix(in srgb,var(--c) 60%,var(--card))}
.art .ln{stroke:var(--ink);stroke-width:2.5;fill:none;stroke-linecap:round;stroke-linejoin:round}
.art .lc{stroke:var(--c);stroke-width:3;fill:none;stroke-linecap:round}
.art .ok{fill:var(--ink)} .art text{font-family:var(--f-display);font-weight:700;fill:var(--ink)}
.art .tc{fill:var(--c)}
.hero{position:relative;overflow:hidden;display:grid;grid-template-columns:1.15fr 1fr;gap:12px;align-items:center;border-radius:20px;padding:28px clamp(18px,4vw,40px);
  background:linear-gradient(135deg,color-mix(in srgb,var(--tim) 18%,var(--card)) 0%,color-mix(in srgb,var(--vang) 16%,var(--card)) 100%);border:1px solid var(--line)}
.hero h1{font-size:clamp(1.9rem,5vw,3rem);color:var(--tim);font-weight:800}
.hero p{margin:6px 0 16px;color:var(--ink-soft);max-width:44ch;font-size:1.05rem}
.hero .art{width:100%;max-width:420px;height:auto;justify-self:center}
.hero .hang .btn{box-shadow:0 4px 0 color-mix(in srgb,var(--tim) 55%,#000)}
.hero .hang .btn:active{transform:translateY(3px);box-shadow:0 1px 0 color-mix(in srgb,var(--tim) 55%,#000)}
.hero .btn.phu{box-shadow:inset 0 0 0 2px var(--tim)!important;background:var(--card)}
.nhanh{display:flex;flex-wrap:wrap;gap:8px;margin-top:14px}
.nhanh span{background:var(--card);border:1px solid var(--line);border-radius:999px;padding:4px 12px;font-size:.85rem;color:var(--ink-soft)}
.nhanh b{color:var(--tim);font-family:var(--f-display)}
.dsc button .dot-c{width:10px;height:10px;border-radius:50%;background:var(--c);flex:none;align-self:center}
.dsc button[aria-pressed="true"]{box-shadow:0 0 0 2px var(--c)}
.bia{display:grid;grid-template-columns:1fr auto;gap:16px;align-items:center;margin:-28px calc(-1*clamp(18px,4vw,40px)) 18px;padding:22px clamp(18px,4vw,40px);
  border-radius:var(--r) var(--r) 0 0;background:linear-gradient(120deg,color-mix(in srgb,var(--c) 22%,var(--card)),color-mix(in srgb,var(--c) 6%,var(--card)));border-bottom:3px solid var(--c)}
.bia .art{width:150px;height:auto}
.bia h2{font-size:clamp(1.6rem,3.5vw,2.3rem);color:var(--ink)}
.bia .eyebrow{color:var(--c)}
.baihoc h3{color:var(--c);display:flex;align-items:center;gap:8px}
.baihoc h3::before{content:"";width:8px;height:22px;border-radius:4px;background:var(--c)}
.baihoc .rule{background:color-mix(in srgb,var(--c) 12%,var(--card));border:1px solid color-mix(in srgb,var(--c) 30%,var(--card))}
.baihoc .rule b{color:var(--c)}
.chip{flex-direction:row;align-items:center;gap:12px;border-left:5px solid var(--c);transition:transform .15s}
.chip:hover{transform:translateY(-2px);box-shadow:0 6px 16px color-mix(in srgb,var(--c) 22%,transparent)}
.chip .art{width:56px;height:42px;flex:none}
.chip .chu{display:flex;flex-direction:column;gap:2px;min-width:0}
.chip .so{color:var(--c)}
.chip[aria-pressed="true"]{border-color:var(--c);box-shadow:0 0 0 2px var(--c);background:color-mix(in srgb,var(--c) 8%,var(--card))}
.thanh-tien{height:6px;border-radius:3px;background:var(--line);overflow:hidden;margin-top:4px}
.thanh-tien i{display:block;height:100%;background:var(--c)}
.cauhoi{border-top:6px solid var(--c);box-shadow:0 10px 30px color-mix(in srgb,var(--c) 12%,transparent)}
.cauhoi .dau{display:flex;gap:14px;align-items:center}
.cauhoi .dau .art{width:64px;height:48px;flex:none}
.phan{flex-direction:row;gap:12px;align-items:flex-start}
.phan .owl{width:64px;height:64px;flex:none}
.phan .noi{display:flex;flex-direction:column;gap:4px;min-width:0}
.ketqua .owl{width:110px;height:110px}
.ketqua{grid-template-columns:auto 1fr auto}
.game{border-top:6px solid var(--do);background:linear-gradient(180deg,color-mix(in srgb,var(--do) 8%,var(--card)),var(--card) 40%)}
.game .art{width:220px;height:auto;margin:0 auto}
.game .phep{color:var(--tim)}
.game .phep.nay{animation:nay .35s}
@keyframes nay{40%{transform:scale(1.12);color:var(--xanh)}}
#phaoGiay{position:fixed;inset:0;pointer-events:none;z-index:50}

@media (max-width:820px){
  .hero{grid-template-columns:1fr}
  .hero .art{max-width:300px;order:-1}
  .ketqua{grid-template-columns:auto 1fr}
  .ketqua .owl{display:none}
  .hoc{grid-template-columns:1fr}
  .dsc{position:static}
  .dsc .nhom{display:none}
  .dsc select{display:block}
  .the{grid-template-columns:repeat(2,1fr)}
  .thanh{grid-template-columns:minmax(0,1fr) 5em 3.5em}
}
@media (max-width:480px){
  .ketqua{grid-template-columns:1fr;justify-items:center;text-align:center}
  .tabs a{padding:5px 9px;font-size:.88rem}
}
@media (prefers-reduced-motion:reduce){*{animation:none!important;transition:none!important}}

/* Màn hình chọn lớp */
.chon-lop{min-height:100vh;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:28px;padding-block:32px;text-align:center}
.chon-lop h1{font-size:clamp(2.2rem,7vw,3.6rem);color:var(--tim);font-weight:800}
.chon-lop .lead{margin:0 auto}
.the-lop{display:grid;grid-template-columns:repeat(2,minmax(0,300px));gap:20px;justify-content:center;width:100%}
.the-lop>button,.the-lop .the-con>button[data-con]{display:flex;flex-direction:column;align-items:center;gap:10px;padding:26px 20px;border-radius:22px;border:2px solid var(--line);background:var(--card);cursor:pointer;color:var(--ink);transition:transform .15s,box-shadow .15s;border-bottom:7px solid var(--c)}
.the-lop>button:hover,.the-lop .the-con>button[data-con]:hover{transform:translateY(-4px);box-shadow:0 12px 28px color-mix(in srgb,var(--c) 25%,transparent)}
.the-lop .so-lop{font-family:var(--f-display);font-weight:800;font-size:4.2rem;line-height:1;color:var(--c)}
.the-lop .ten-lop{font-family:var(--f-display);font-weight:700;font-size:1.4rem}
.the-lop .phu-de{font-size:.88rem;color:var(--ink-soft)}
.the-lop .owl{width:84px;height:84px}
.doi-lop{border:0;background:var(--tim-nhat);color:var(--tim);font-weight:700;padding:6px 14px;border-radius:999px;cursor:pointer;font-size:.88rem}
@media (max-width:560px){.the-lop{grid-template-columns:1fr}}

/* Đăng nhập, chọn con, PIN */
.o-form{display:flex;flex-direction:column;gap:8px;width:100%;max-width:420px;text-align:left;background:var(--card);border:1px solid var(--line);border-radius:16px;padding:20px 22px}
.o-form summary{cursor:pointer;font-weight:700;color:var(--tim)}
.o-form label{font-weight:600;font-size:.9rem}
.o-form input,.o-form select{font-size:1.05rem;padding:10px 12px;border-radius:10px;border:2px solid var(--line);background:var(--paper)}
.o-form input:focus,.o-form select:focus{border-color:var(--tim);outline:none}
.o-pin{font-family:var(--f-display);font-size:2.4rem!important;letter-spacing:.5em;text-align:center;width:9ch;padding-left:.5em!important}
.loi{margin:0;color:var(--do);font-size:.92rem}
.lien-ket{border:0;background:none;color:var(--tim);text-decoration:underline;cursor:pointer;padding:4px;align-self:flex-start}
.nguoi-hoc b{color:var(--tim)}
.chon-lop>.owl{width:110px;height:110px}

/* Đăng nhập thân thiện: tranh + thẻ đăng nhập */
.chon-lop.dn{justify-content:flex-start;padding-block:28px}
.dn-khung{display:grid;grid-template-columns:1.1fr 1fr;gap:28px;align-items:center;width:100%;max-width:1000px;text-align:left}
.dn-tranh .tranh{width:100%;height:auto;display:block;border-radius:28px;box-shadow:0 18px 40px color-mix(in srgb,var(--tim) 18%,transparent)}
.dn-tranh.nho{width:min(360px,100%)}
.dn-the{display:flex;flex-direction:column;gap:14px;min-width:0}
.dn-dau h1{font-size:clamp(2.2rem,6vw,3.2rem);color:var(--tim);font-weight:800}
.dn-dau .lead{margin:4px 0 0}
.dn-tieu{font-size:1.6rem;color:var(--ink)}
.dn-the .o-form{max-width:none}
.tab-dn{display:grid;grid-template-columns:1fr 1fr;background:var(--tim-nhat);border-radius:999px;padding:4px;gap:4px}
.tab-dn button{border:0;background:none;border-radius:999px;padding:9px 12px;font-weight:700;color:var(--tim);cursor:pointer}
.tab-dn button.dang{background:var(--card);box-shadow:0 2px 8px color-mix(in srgb,var(--tim) 20%,transparent)}
.btn.to{width:100%;padding:13px 20px;font-size:1.08rem;margin-top:4px;box-shadow:0 4px 0 color-mix(in srgb,var(--tim) 55%,#000)}
.btn.to:active{transform:translateY(3px);box-shadow:0 1px 0 color-mix(in srgb,var(--tim) 55%,#000)}
.btn.google{width:100%;background:var(--card);color:var(--ink);box-shadow:inset 0 0 0 2px var(--line);padding:12px 20px}
.hoac{display:flex;align-items:center;gap:10px;color:var(--ink-soft);font-size:.85rem}
.hoac::before,.hoac::after{content:"";flex:1;height:1px;background:var(--line)}
.o-mk{display:flex;gap:6px}.o-mk input{flex:1;min-width:0}
.hien-mk{border:2px solid var(--line);background:var(--card);border-radius:10px;padding:0 12px;cursor:pointer;color:var(--ink-soft);font-weight:600}
.goi-y{margin:-2px 0 4px;font-size:.82rem;color:var(--ink-soft)}
.goi-y.tot,.loi.tot{color:var(--xanh)}
.thanh-tk{display:flex;flex-wrap:wrap;justify-content:space-between;gap:8px;width:100%;max-width:900px;font-size:.9rem;color:var(--ink-soft);background:var(--card);border:1px solid var(--line);border-radius:999px;padding:6px 16px}
.thanh-tk .lien-ket{align-self:center}
/* Hình đại diện */
.avatar{width:96px;height:96px;filter:drop-shadow(0 6px 10px rgba(0,0,0,.12))}
.avatar.to{width:132px;height:132px}
.avatar.nho{width:34px;height:34px;filter:none;align-self:center}
.brand{align-items:center}
.the-lop .nhan-lop{font-family:var(--f-display);font-weight:700;color:var(--c);background:color-mix(in srgb,var(--c) 14%,var(--card));padding:2px 14px;border-radius:999px}
.them-con{max-width:560px}
.nhan{font-weight:600;font-size:.9rem}
.chon-avatar{display:flex;flex-direction:column;gap:8px}
.tabs-avatar{display:flex;flex-wrap:wrap;gap:6px}
.tab-avatar{border:2px solid var(--line);background:var(--card);border-radius:999px;padding:4px 12px;font-weight:700;font-size:.85rem;cursor:pointer;color:var(--ink-soft)}
.tab-avatar small{opacity:.7;font-weight:600}
.tab-avatar[aria-pressed="true"]{border-color:var(--tim);background:var(--tim-nhat);color:var(--tim)}
.luoi-avatar{display:grid;grid-template-columns:repeat(auto-fill,minmax(82px,1fr));gap:8px;max-height:340px;overflow-y:auto;padding:2px 4px 2px 2px;overscroll-behavior:contain}
.luoi-avatar label span{text-align:center;line-height:1.25}
.chon-avatar label{display:flex;flex-direction:column;align-items:center;gap:2px;padding:8px 4px;border:2px solid var(--line);border-radius:14px;cursor:pointer;font-size:.75rem;color:var(--ink-soft);background:var(--paper)}
.chon-avatar input{position:absolute;opacity:0;pointer-events:none}
.chon-avatar .avatar{width:52px;height:52px}
.chon-avatar label:has(input:checked){border-color:var(--tim);background:var(--tim-nhat);color:var(--tim);font-weight:700}
.chon-avatar label:has(input:focus-visible){outline:3px solid var(--tim);outline-offset:2px}
/* Bàn phím PIN */
.pin-khung{display:flex;flex-direction:column;align-items:center;gap:10px}
.cham-pin{display:flex;gap:16px;margin:6px 0}
.cham-pin i{width:20px;height:20px;border-radius:50%;border:3px solid var(--tim);transition:background .12s}
.cham-pin i.co{background:var(--tim)}
.cham-pin.lac{animation:lac .35s}
.ban-phim{display:grid;grid-template-columns:repeat(3,76px);gap:12px;margin-top:6px}
.ban-phim button{height:76px;border-radius:22px;border:0;background:var(--card);box-shadow:0 4px 0 var(--line),inset 0 0 0 2px var(--line);font-family:var(--f-display);font-size:2rem;font-weight:700;color:var(--tim);cursor:pointer}
.ban-phim button:active{transform:translateY(3px);box-shadow:0 1px 0 var(--line),inset 0 0 0 2px var(--line)}
.ban-phim button.phu{color:var(--ink-soft);font-size:1.5rem}
@media (max-width:820px){.dn-khung{grid-template-columns:1fr}.dn-tranh{max-width:420px;margin:0 auto}}
@media (max-width:420px){.ban-phim{grid-template-columns:repeat(3,64px)}.ban-phim button{height:64px}}
.chan-dn{margin:0;font-size:.82rem;color:var(--ink-soft);text-align:center}
.chan-dn a{color:var(--ink-soft)}
/* Hồ sơ con: thẻ có nút Sửa, form hai cột, vùng xóa */
.the-con{position:relative;display:flex}
.the-con>button[data-con]{flex:1}
.sua-con{position:absolute;top:10px;right:10px;border:1px solid var(--line);background:var(--card);color:var(--ink-soft);border-radius:999px;padding:3px 12px;font-size:.8rem;font-weight:600;cursor:pointer}
.sua-con:hover{color:var(--tim);border-color:var(--tim)}
.hai-cot{display:grid;grid-template-columns:1fr 1fr;gap:10px}
.hai-cot>div{display:flex;flex-direction:column;gap:8px;min-width:0}
.tuy-chon{font-weight:400;color:var(--ink-soft);font-size:.82rem}
.vung-xoa{border-top:1px dashed var(--line);margin-top:10px;padding-top:10px}
.vung-xoa p{margin:0 0 8px}
.lien-ket.do{color:var(--do)}
.btn.do{background:var(--do)}
@media (max-width:420px){.hai-cot{grid-template-columns:1fr}}
/* Trang quản trị */
.qt{display:flex;flex-direction:column;gap:16px;width:100%;max-width:1100px;text-align:left}
.qt #qtNoiDung{display:flex;flex-direction:column;gap:16px}
.qt-the{grid-template-columns:repeat(3,1fr)}
.cot-ngay{display:flex;gap:6px;align-items:flex-end;height:170px;overflow-x:auto}
.cot-ngay>div{flex:1;min-width:34px;height:100%;display:flex;flex-direction:column;justify-content:flex-end;align-items:center;gap:4px}
.cot-ngay i{display:block;width:70%;background:var(--tim);border-radius:6px 6px 0 0}
.cot-ngay .so{font-size:.75rem;font-weight:700;color:var(--tim)}
.o-tim{padding:8px 12px;border-radius:10px;border:2px solid var(--line);background:var(--paper);min-width:0;flex:0 1 280px;font-size:.92rem}
.qt-bang td{font-size:.86rem}
.huy-hieu{display:inline-block;margin:4px 4px 0 0;padding:1px 9px;border-radius:999px;font-size:.72rem;font-weight:700;background:var(--tim-nhat);color:var(--tim)}
.huy-hieu.qt-hh{background:var(--vang-nhat);color:var(--vang)}
.huy-hieu.khoa{background:var(--do-nhat);color:var(--do)}
.huy-hieu.mo{background:var(--xanh-nhat);color:var(--xanh)}
.chip-con{display:inline-flex;align-items:center;gap:4px;margin:2px 6px 2px 0;padding:2px 8px 2px 2px;border:1px solid var(--line);border-radius:999px;background:var(--paper)}
.avatar.mini{width:22px;height:22px;filter:none}
.thao-tac{white-space:nowrap}
.nho-btn{padding:5px 12px;font-size:.82rem}
.xac-nhan td{background:var(--do-nhat)}
.xac-nhan p{margin:0 0 8px}
@media (max-width:820px){.qt-the{grid-template-columns:repeat(2,1fr)}}
.qt .thanh-tk{max-width:none}
/* Góp ý */
.gy{display:flex;flex-direction:column;gap:16px;width:100%;max-width:820px;text-align:left}
.gy .thanh-tk{max-width:none}
.gy-dau{display:flex;gap:16px;align-items:center}
.gy-dau .owl{width:96px;height:96px;flex:none}
.gy-dau h1{font-size:clamp(1.6rem,4vw,2.2rem);color:var(--tim)}
.gy-form{max-width:none}
.gy-form textarea,.bao-sai-form textarea,.gy-xu-ly textarea{font:inherit;font-size:1rem;padding:10px 12px;border-radius:10px;border:2px solid var(--line);background:var(--paper);resize:vertical;min-width:0}
.gy-form textarea:focus,.bao-sai-form textarea:focus{border-color:var(--tim);outline:none}
.chon-loai{display:flex;flex-wrap:wrap;gap:8px}
.chon-loai label{cursor:pointer}
.chon-loai input{position:absolute;opacity:0;pointer-events:none}
.chon-loai span{display:inline-block;padding:7px 14px;border-radius:999px;border:2px solid var(--line);background:var(--paper);font-weight:600;font-size:.9rem}
.chon-loai label:has(input:checked) span{border-color:var(--tim);background:var(--tim-nhat);color:var(--tim)}
.chon-loai label:has(input:focus-visible) span{outline:3px solid var(--tim);outline-offset:2px}
.sao{display:flex;align-items:center;gap:4px}
.sao button{border:0;background:none;font-size:2rem;line-height:1;color:var(--line);cursor:pointer;padding:0 2px}
.sao button.co{color:#f2a93b}
.sao-nho{color:#f2a93b;margin-left:6px;letter-spacing:1px}
.gy-muc{border:1px solid var(--line);border-radius:12px;padding:12px 14px;display:flex;flex-direction:column;gap:6px;background:var(--paper)}
.gy-muc p{margin:0;white-space:pre-wrap}
.tra-loi{background:var(--xanh-nhat);border-radius:8px;padding:8px 10px;font-size:.92rem}
.huy-hieu.tt-moi{background:var(--vang-nhat);color:var(--vang)}
.huy-hieu.tt-dang-xu-ly{background:var(--tim-nhat);color:var(--tim)}
.huy-hieu.tt-da-xong{background:var(--xanh-nhat);color:var(--xanh)}
.ngu-canh{background:var(--card);border:1px dashed var(--line);border-radius:8px;padding:8px 10px;font-size:.88rem}
.gy-xu-ly{display:grid;grid-template-columns:auto 1fr auto auto;gap:8px;align-items:start}
.gy-xu-ly select{padding:7px 10px;border-radius:10px;border:2px solid var(--line);background:var(--card)}
.loc-gy{display:flex;flex-wrap:wrap;gap:6px}
.loc-gy button{border:1px solid var(--line);background:var(--card);border-radius:999px;padding:4px 12px;font-size:.82rem;cursor:pointer;color:var(--ink-soft)}
.loc-gy button.dang{background:var(--tim);color:var(--card);border-color:var(--tim)}
.bao-sai{margin-left:auto;font-size:.88rem;color:var(--ink-soft)}
.bao-sai-form{max-width:none;margin-top:10px;background:var(--paper)}
@media (max-width:620px){.gy-xu-ly{grid-template-columns:1fr}}

/* ===== Kiểu nút theo đề xuất của Gemini (19/10/2026) — đặt cuối file để thắng các kiểu nút cũ ===== */
.btn,.hero .hang .btn{min-height:48px;padding:10px 24px;border-radius:14px;border:2px solid transparent;
  font-family:var(--f-display);font-weight:800;letter-spacing:.01em;
  box-shadow:0 4px 10px color-mix(in srgb,var(--tim) 25%,transparent);
  transition:transform .2s cubic-bezier(.4,0,.2,1),box-shadow .2s,background-color .2s,color .2s,border-color .2s}
.btn:hover,.hero .hang .btn:hover{transform:translateY(-2px);filter:brightness(1.05);box-shadow:0 6px 14px color-mix(in srgb,var(--tim) 35%,transparent)}
.btn:active,.hero .hang .btn:active{transform:translateY(0);box-shadow:0 2px 4px color-mix(in srgb,var(--tim) 20%,transparent)}
.btn:disabled,.btn:disabled:hover{transform:none;filter:none;box-shadow:none}
.btn.phu,.hero .btn.phu{background:var(--card);color:var(--ink);border-color:var(--line);box-shadow:0 2px 4px rgba(30,27,75,.06)!important}
.btn.phu:hover,.hero .btn.phu:hover{border-color:var(--tim);color:var(--tim);background:var(--tim-nhat)}
.btn.to{min-height:52px;font-size:1.1rem;box-shadow:0 4px 10px color-mix(in srgb,var(--tim) 25%,transparent)}
.btn.to:active{transform:translateY(0);box-shadow:0 2px 4px color-mix(in srgb,var(--tim) 20%,transparent)}
.btn.do{background:var(--do);color:#fff;box-shadow:0 4px 10px color-mix(in srgb,var(--do) 25%,transparent)}
.btn.do:hover{box-shadow:0 6px 14px color-mix(in srgb,var(--do) 35%,transparent)}
.btn.google{background:#fff;color:#374151;border:2px solid var(--line);box-shadow:0 2px 4px rgba(30,27,75,.06)}
.btn.google:hover{background:#f9fafb;border-color:#d1d5db;filter:none}
.nho-btn,.btn.nho-btn{min-height:36px;padding:6px 14px;font-size:.875rem;border-radius:10px}
.btn{color:#fff}
.btn.phu,.btn.google{color:var(--ink)}
@media (prefers-color-scheme: dark){:root:not([data-theme="light"]) .btn{color:#1e1b4b}:root:not([data-theme="light"]) .btn.phu{color:var(--ink)}}
:root[data-theme="dark"] .btn{color:#1e1b4b}
:root[data-theme="dark"] .btn.phu{color:var(--ink)}
@media (prefers-reduced-motion:reduce){.btn:hover,.hero .hang .btn:hover{transform:none}}
/* Nút mang màu riêng của chương (gán trong style) luôn chữ trắng, kể cả chế độ tối */
.btn[style*="background"]{color:#fff!important}
/* Nunito rộng hơn Baloo: giữ tên trang trên một dòng, ẩn dòng phụ trên điện thoại */
.brand b{white-space:nowrap}
@media (max-width:600px){.brand>span{display:none}.brand b{font-size:1.3rem}}

/* Bảng xếp hạng */
.xh{display:flex;flex-direction:column;gap:12px;max-width:760px;margin:0 auto}
.xh-dau{display:flex;flex-wrap:wrap;gap:12px;align-items:end;justify-content:space-between}
.xh-dau h1{font-size:clamp(1.7rem,4vw,2.3rem);color:var(--tim)}
.xh .lead{margin:0}
.xh-ds{list-style:none;margin:0;padding:0;display:flex;flex-direction:column;gap:8px}
.xh-dong{display:grid;grid-template-columns:44px 48px 1fr auto;gap:12px;align-items:center;background:var(--card);border:1px solid var(--line);border-radius:14px;padding:8px 14px}
.xh-hang{font-family:var(--f-display);font-weight:900;font-size:1.2rem;color:var(--ink-soft);text-align:center;width:36px;height:36px;line-height:36px;border-radius:50%}
.avatar.xh-av{width:44px;height:44px;filter:none}
.xh-ten{font-weight:700;min-width:0;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.xh-diem{color:var(--ink-soft);font-size:.88rem;white-space:nowrap}
.xh-diem b{font-family:var(--f-display);font-size:1.3rem;color:var(--tim)}
.xh-dong.huy-chuong .xh-hang{color:#fff}
.xh-dong.h1 .xh-hang{background:#e0a100}
.xh-dong.h2 .xh-hang{background:#94a3b8}
.xh-dong.h3 .xh-hang{background:#c2703d}
.xh-dong.h1{border-color:#e0a100;box-shadow:0 4px 14px color-mix(in srgb,#e0a100 22%,transparent)}
.xh-dong.la-con{background:var(--tim-nhat);border:2px solid var(--tim)}
.xh-ngoai{margin:6px 0 0}
.xh .trong .owl{width:90px;height:90px}
.o-tick{display:flex;flex-wrap:wrap;align-items:center;gap:8px;font-weight:600;font-size:.92rem;cursor:pointer}
.o-tick input{width:20px;height:20px;accent-color:var(--tim)}
@media (max-width:480px){.xh-dong{grid-template-columns:34px 40px 1fr auto;gap:8px;padding:8px 10px}.avatar.xh-av{width:38px;height:38px}}

/* Nút chuyển Sáng / Tối / Theo máy (js/che-do.js) — nổi ở góc dưới bên phải */
.nut-che-do{position:fixed;z-index:40;right:max(14px,env(safe-area-inset-right,0px));bottom:calc(14px + env(safe-area-inset-bottom,0px));
  display:inline-flex;align-items:center;gap:6px;min-height:44px;padding:8px 14px 8px 12px;border-radius:999px;border:1px solid var(--line);
  background:var(--card);color:var(--ink);font:600 .82rem var(--f-body);cursor:pointer;box-shadow:0 6px 16px rgba(30,27,75,.14);opacity:.92}
.nut-che-do:hover{opacity:1;border-color:var(--tim);color:var(--tim)}
.nut-che-do svg{width:20px;height:20px;fill:none;stroke:currentColor;stroke-width:2;stroke-linecap:round;stroke-linejoin:round}
.nut-che-do svg path[d^="M20 14.5"]{fill:currentColor;stroke:none}
@media (max-width:600px){.nut-che-do span{display:none}.nut-che-do{padding:10px;width:44px;justify-content:center}}