:root{--ink:#16202e;--ink-2:#3d4a5c;--muted:#5a6578;--line:#e3e6eb;--bg:#f4f5f7;--card:#ffffff;--brand:#0f6e6a;--brand-dark:#0a4f4c;--brand-tint:#e2f1ef;--navy:#16202e;--navy-2:#24314a;--warn-bg:#fff8ec;--warn:#9a3e00;--good:#0a6b3d;--danger-bg:#fff4f0;--danger:#8a2c0d;--radius:14px;--font-zh:"PingFang SC","Hiragino Sans GB","Microsoft YaHei","Noto Sans SC",system-ui,sans-serif;--font-en:system-ui,-apple-system,"Segoe UI",Roboto,"Helvetica Neue",Arial,"PingFang SC","Microsoft YaHei",sans-serif}*{box-sizing:border-box}body,html{margin:0;padding:0}body{font-family:var(--font-zh);color:var(--ink);background:var(--card);line-height:1.6}body.student{font-family:var(--font-en);background:#f5f8f7}a{color:var(--brand)}a:hover{color:var(--brand-dark)}button,input,textarea{font:inherit}h1,h2,h3{line-height:1.25;margin:0}p{margin:0}.container{max-width:1200px;margin:0 auto;padding:0 24px}.row{flex-wrap:wrap;gap:16px;align-items:center}.row,.stack{display:flex}.stack{flex-direction:column;gap:12px}.grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));grid-gap:18px;gap:18px}.muted{color:var(--muted)}.small{font-size:13px}.sr-only{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}.btn{display:inline-flex;align-items:center;justify-content:center;min-height:44px;padding:10px 18px;border-radius:10px;border:1px solid transparent;text-decoration:none;cursor:pointer;font-weight:500}.btn-primary{background:var(--brand);color:#fff}.btn-primary:hover{background:var(--brand-dark);color:#fff}.btn-outline{border-color:#cdd3db}.btn-light,.btn-outline{background:#fff;color:var(--ink)}.btn-light{font-weight:700}.btn:disabled{opacity:.6;cursor:not-allowed}.card{background:var(--card);border:1px solid 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a.active{background:var(--brand);color:#fff}.sidebar.light .nav a.active{background:var(--brand-tint);color:var(--brand-dark)}.child-btn{display:flex;align-items:center;gap:10px;width:100%;text-align:left;background:transparent;border:1px solid #2e3b52;color:#c3ccd8;border-radius:12px;padding:10px 12px;cursor:pointer;min-height:44px}.child-btn.selected{background:var(--navy-2);border-color:#3a4a66;color:#fff}.avatar{width:34px;height:34px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-weight:700;background:var(--brand-tint);color:var(--brand);flex-shrink:0}.main{flex:999 1 560px;min-width:0;display:flex;flex-direction:column}.main-header{display:flex;flex-wrap:wrap;gap:12px;align-items:center;padding:16px 28px;background:#fff;border-bottom:1px solid var(--line)}.main-body{flex-grow:1;padding:24px 28px;display:flex;flex-direction:column;gap:18px;max-width:900px;width:100%;margin:0 auto}.msg{max-width:80%;padding:12px 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