/* Khung chung của trang chủ học sinh (index.html) và các trang lớp (lop/…). Giao diện theo trang tu-vung/. */
:root{--ink:#111;--line:#555;--head:#d9d9d9;--sub:#efefef;--muted:#666;--bg:#fff;--pur:#53468F;--pur2:#EFEAF8;--gold:#C99A2E;--ok:#2f7a4f;--okb:#e6f3eb;--bad:#b0283c;--badb:#fbe9ec}
*{box-sizing:border-box}
[hidden]{display:none!important}
body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.45 "Times New Roman",Times,"Noto Serif KR","Malgun Gothic",serif}
main{max-width:900px;margin:0 auto;padding:16px 16px 48px}
.ko,.kr{font-family:"Noto Sans KR","Malgun Gothic","Apple SD Gothic Neo",sans-serif}

/* Đầu trang: logo + menu lớp + Về cô */
.brand{display:grid;grid-template-columns:auto 1fr auto;grid-template-areas:"logo lop co";align-items:center;gap:10px 16px;padding:0 0 12px;margin:0 0 14px;border-bottom:1px solid #d8dde6}
.brand>.lg{grid-area:logo}
.brand .logo{display:block;height:88px;width:auto;margin:0 0 2px -6px}
.brand .zl{display:block;font-size:15px;color:var(--muted)}
.brand .zl a{color:inherit;text-decoration:none;border-bottom:1px dotted var(--muted)}
.lop{grid-area:lop;display:flex;flex-wrap:wrap;justify-content:flex-end;gap:6px}
.lop a{border:1px solid var(--pur);color:var(--pur);padding:5px 12px;border-radius:16px;text-decoration:none;font-size:15px;font-weight:bold;white-space:nowrap}
.lop a.on{background:var(--pur);color:#fff}
.lop a.kh{border-style:dashed;font-weight:normal}
.co{grid-area:co;flex:none;display:flex;flex-direction:column;align-items:center;gap:3px;text-decoration:none;color:var(--pur);font:12px Arial,sans-serif}
.co i{width:42px;height:42px;border-radius:50%;background:var(--pur);color:#fff;display:grid;place-items:center;font:bold 18px Georgia,serif;font-style:normal}
@media (max-width:719px){
  .brand{grid-template-columns:1fr auto;grid-template-areas:"logo co" "lop lop"}
  .brand .logo{height:74px}
  .lop a{font-size:14px;padding:4px 9px}
  .lop{gap:6px 5px;justify-content:flex-start}
}

h1{font-size:26px;margin:4px 0 4px}
/* Tiêu đề lớp: tên (sách) · khẩu hiệu lớp · nguyên tắc chung */
.hd{margin:2px 0 14px}
.hd h1{color:var(--pur);font-size:28px;line-height:1.2;margin:0 0 4px}
.hd h1 span{font-size:19px;font-weight:normal;color:var(--muted);white-space:nowrap}
.hd .sl{margin:0;font-size:18px;font-weight:bold;color:var(--gold)}
.hd .nt{margin:8px 0 0;padding-top:8px;border-top:1px solid #d8dde6;font-size:15px;color:var(--muted)}
@media (max-width:479px){.hd h1{font-size:24px}.hd h1 span{font-size:16px}.hd .sl{font-size:16px}}
.intro{margin:0 0 12px;color:var(--muted);font-size:15px}
h2{font-size:24px;margin:14px 0 4px}
h2 small{font-size:16px;font-weight:normal;color:var(--muted)}
h3{font-size:18px;margin:18px 0 6px}

/* Đọc · Nghe · Viết */
.parts{display:grid;grid-template-columns:repeat(6,1fr);gap:2px;background:var(--pur);margin:0 0 10px;border:2px solid var(--pur);border-radius:8px;overflow:hidden}
@media (max-width:639px){.parts{grid-template-columns:repeat(3,1fr)}}
.parts button{min-width:0;font:inherit;font-size:17px;font-weight:bold;padding:8px 4px;border:0;background:var(--bg);color:var(--pur);cursor:pointer}
.parts button.on{background:var(--pur);color:#fff}
.parts small{display:block;font-weight:normal;font-size:12.5px}

/* Thanh chọn dạng câu */
nav.dang{display:flex;flex-wrap:wrap;gap:6px;margin:0 -16px 10px;padding:8px 16px;position:sticky;top:0;background:var(--bg);border-bottom:1px solid var(--line);z-index:2}
nav.dang a{border:1px solid var(--line);padding:4px 12px;border-radius:16px;color:var(--ink);text-decoration:none;font-size:15px}
nav.dang a.on{background:var(--pur);border-color:var(--pur);color:#fff;font-weight:bold}

/* Thẻ Từ vựng · Học liệu · Câu đề thi */
.tabs{display:flex;gap:0;border-bottom:2px solid var(--pur);margin:8px 0 14px}
.tabs button{font:inherit;font-size:16px;padding:7px 14px;border:2px solid transparent;border-bottom:0;background:none;color:var(--muted);cursor:pointer;border-radius:8px 8px 0 0;margin-bottom:-2px}
.tabs button.on{border-color:var(--pur);background:var(--bg);color:var(--pur);font-weight:bold;border-bottom:2px solid var(--bg)}
.tabs small{font-size:12px;color:var(--muted);font-weight:normal}
.tools{margin:0 0 12px;font-size:14px;display:flex;gap:8px;flex-wrap:wrap;align-items:center}
.tools button{font:inherit;border:1px solid var(--line);background:var(--sub);padding:4px 12px;border-radius:4px;cursor:pointer}
.tools a{color:var(--pur)}
.empty{color:var(--muted);font-style:italic}

/* Bảng từ (như tu-vung/) */
.tb{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.3fr);border-top:1px solid var(--line);border-left:1px solid var(--line)}
.tb>div{border-right:1px solid var(--line);border-bottom:1px solid var(--line);padding:5px 8px;min-height:32px}
.tb .h{background:var(--head);text-align:center;padding:4px}
.tb .ko{font-size:15px}
.tb .ex{grid-column:1/-1;font-family:"Noto Sans KR","Malgun Gothic",sans-serif;font-size:14px;color:#333;background:#fafafa}
.tb .ex u{text-underline-offset:3px;font-weight:bold}
.hide .vi{color:transparent;background:repeating-linear-gradient(135deg,var(--sub) 0 6px,#fff 6px 12px);cursor:pointer}
.hide .vi.show{color:var(--ink);background:none}
.blk{margin:0 0 18px}
.blk h4{margin:0;padding:6px 10px;background:var(--pur);color:#fff;font-size:16px;font-family:"Noto Sans KR","Malgun Gothic",sans-serif}
.blk h4 small{font-weight:normal;font-size:13px;opacity:.9;font-family:"Times New Roman",serif}

/* Học liệu */
.hl{display:grid;gap:8px}
.hl a{display:flex;gap:12px;align-items:flex-start;border:1px solid var(--line);border-radius:8px;padding:10px 12px;text-decoration:none;color:var(--ink)}
.hl a:hover{border-color:var(--pur);background:var(--pur2)}
.hl .tag{flex:none;font:bold 12px Arial,sans-serif;color:var(--pur);background:var(--pur2);border-radius:4px;padding:3px 6px;margin-top:2px;min-width:78px;text-align:center}
.hl b{display:block;font-size:17px}
.hl small{display:block;color:var(--muted);font-size:14px}

/* Câu đề thi */
.de{border:1px solid var(--line);border-radius:8px;margin:0 0 16px;overflow:hidden}
.de>.t{background:var(--pur2);color:var(--pur);font-weight:bold;padding:6px 12px;font-size:16px}
.de .bd{padding:8px 12px 4px}
.de .gr{font-size:14px;color:var(--muted);margin:0 0 6px}
.de .ps{white-space:pre-line;border:1px solid #ccc;padding:8px 10px;margin:0 0 8px;font-size:15.5px;line-height:1.7}
.de img{max-width:100%;height:auto;display:block;margin:0 0 8px;border:1px solid #ddd}
.de audio{width:100%;margin:0 0 8px}
.q{margin:0 0 14px}
.q .st{font-size:15.5px;margin:0 0 6px}
.q .st b{color:var(--pur);margin-right:6px;font-family:"Times New Roman",serif}
.op{display:grid;grid-template-columns:1fr 1fr;gap:6px}
@media (max-width:639px){.op{grid-template-columns:1fr}}
.op button{text-align:left;font:15px/1.4 "Noto Sans KR","Malgun Gothic",sans-serif;padding:7px 10px;border:1px solid #bbb;border-radius:6px;background:#fff;color:var(--ink);cursor:pointer}
.op button.pick{border-color:var(--pur);background:var(--pur2)}
.op button.ok{border-color:var(--ok);background:var(--okb);color:var(--ok);font-weight:bold}
.op button.bad{border-color:var(--bad);background:var(--badb);color:var(--bad);text-decoration:line-through}
.q .fb{font-size:14px;margin:4px 0 0;color:var(--muted)}
.more{display:block;margin:6px auto 0;font:inherit;font-size:16px;padding:8px 18px;border:2px solid var(--pur);color:var(--pur);background:#fff;border-radius:8px;cursor:pointer}
details.key{margin:4px 0 10px;font-size:15px}
details.key summary{cursor:pointer;color:var(--pur);font-weight:bold}
details.key .kr{white-space:pre-line;background:#fafafa;border:1px solid #ddd;padding:8px 10px;margin-top:6px}

/* Trang lớp */
.lst{display:grid;gap:8px;margin:0 0 16px}
.lst a{display:block;border:1px solid var(--line);border-radius:8px;padding:10px 12px;text-decoration:none;color:var(--ink)}
.lst a:hover{border-color:var(--pur);background:var(--pur2)}
.lst b{display:block;font-size:17px}
.lst small{color:var(--muted);font-size:14px}

footer{margin-top:36px;font-size:14px;color:var(--muted);text-align:center}
footer a{color:var(--pur)}

/* Mã lớp (lop/lop.js) */
.gate{max-width:440px;margin:24px auto;padding:16px 18px;border:2px solid var(--pur);border-radius:10px;background:var(--pur2)}
.gate p{margin:0 0 10px}
.gate form{display:flex;gap:8px}
.gate input{flex:1;min-width:0;font:18px Arial,sans-serif;letter-spacing:2px;text-transform:uppercase;padding:7px 10px;border:1px solid var(--line);border-radius:6px}
.gate button{font:inherit;font-weight:bold;padding:7px 16px;border:0;border-radius:6px;background:var(--pur);color:#fff;cursor:pointer}
.gate .err{color:var(--bad);margin:8px 0 0}
.gate .nt{font-size:14px;color:var(--muted);margin:12px 0 0}
.gate a{color:var(--pur)}

/* Từ vựng · Ngữ pháp · Đề thi */
.chips{display:flex;flex-wrap:wrap;gap:6px;margin:0 0 14px}
.chips a,.chips button{border:1px solid var(--pur);color:var(--pur);background:#fff;border-radius:14px;padding:3px 11px;font:14px "Noto Sans KR","Malgun Gothic",sans-serif;text-decoration:none;cursor:pointer}
.chips .on{background:var(--pur);color:#fff}
h3 a.lt{float:right;font:600 13.5px "Be Vietnam Pro",Arial,sans-serif;color:var(--pur);text-decoration:none;border:1px solid var(--pur);border-radius:14px;padding:2px 10px;margin-top:2px}
.st{font-family:Arial,sans-serif;font-size:11px;color:var(--bad);font-weight:bold;white-space:nowrap;margin-left:4px}
.st.lo{color:var(--muted);font-weight:normal}
.mt{display:block;font-family:Arial,sans-serif;font-size:11.5px;color:var(--muted)}
.hay{margin:0 0 10px;padding:6px 10px;border-left:4px solid var(--pur);background:var(--pur2);font-size:15px}
.dl{display:grid;grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:8px;margin:0 0 16px}
.dl a{display:block;border:1px solid var(--line);border-radius:8px;padding:9px 12px;text-decoration:none;color:var(--ink)}
.dl a:hover{border-color:var(--pur);background:var(--pur2)}
.dl b{display:block;font-size:16px}
.dl small{color:var(--muted);font-size:13.5px}
.dl .sc{color:var(--ok);font-weight:bold}
.back{display:inline-block;margin:0 0 8px;color:var(--pur);font-size:15px}
.score{border:2px solid var(--ok);background:var(--okb);border-radius:8px;padding:10px 14px;margin:0 0 14px;font-size:17px}
.score b{color:var(--ok);font-size:22px}
.submit{display:block;margin:10px auto 0;font:inherit;font-size:17px;font-weight:bold;padding:10px 26px;border:0;background:var(--pur);color:#fff;border-radius:8px;cursor:pointer}
.submit.ghost{background:#fff;color:var(--pur);border:2px solid var(--pur);font-weight:normal;font-size:15px;padding:7px 18px}
.bar{position:sticky;bottom:0;background:var(--bg);border-top:1px solid var(--line);padding:8px 0;margin:0 0 8px;display:flex;gap:10px;align-items:center;justify-content:space-between;font-size:15px}
.bar .submit{margin:0}

/* Trang lớp Seoul (lop/khung.js): 5 phần, thanh chọn bài theo cuốn */
.parts.p5{grid-template-columns:repeat(5,1fr)}
@media (max-width:639px){.parts.p5 button{font-size:15px;padding:7px 2px}.parts.p5 small{font-size:11.5px}}
nav.dang .bk{align-self:center;font:bold 13px Arial,sans-serif;color:var(--gold);margin:0 -2px 0 4px}
nav.dang .bk:first-child{margin-left:0}
@media (max-width:639px){nav.dang:has(.bk) a{padding:3px 9px;font-size:14px}}