:root{--ink:#173957;--blue:#176da0;--sky:#e9f5fa;--paper:#fff;--line:#d7e5ed;--muted:#658094;--good:#12744f;--warn:#c77b14;--danger:#b93a44;font-family:"Microsoft YaHei","PingFang SC",system-ui,sans-serif;color:var(--ink);background:#eff6f8}*{box-sizing:border-box}body{margin:0;min-height:100vh;background:linear-gradient(155deg,#e5f3f8 0,#f8fbfc 48%,#eaf3f6 100%)}button,input,textarea{font:inherit}button{cursor:pointer}.top{padding:26px max(5vw,22px);background:linear-gradient(120deg,#133b5c,#1874a5);color:#fff}.top h1{margin:3px 0;font-size:clamp(24px,4vw,36px)}.top p{margin:5px 0 0;opacity:.84}.eyebrow{font-size:12px;letter-spacing:.14em;opacity:.78}.shell{max-width:1100px;margin:0 auto;padding:28px 20px 70px}.grid{display:grid;grid-template-columns:1fr 1fr;gap:18px}.card{background:rgba(255,255,255,.92);border:1px solid rgba(142,181,201,.35);border-radius:19px;padding:21px;box-shadow:0 12px 34px rgba(37,82,105,.09)}.card h2{font-size:18px;margin:0 0 13px}.card h3{font-size:15px;margin:20px 0 8px}.wide{grid-column:1/-1}.field{display:grid;gap:6px;margin:10px 0}.field label{font-weight:700;font-size:13px}.field input,.field textarea{border:1px solid #bed3df;border-radius:10px;padding:10px 11px;color:var(--ink);background:#fff}.field input:focus,.field textarea:focus{outline:3px solid #a5d8ef;border-color:transparent}.row{display:flex;gap:9px;align-items:center;flex-wrap:wrap}.primary,.secondary,.danger{border:0;border-radius:10px;padding:10px 13px;font-weight:700}.primary{color:#fff;background:var(--blue)}.primary:hover{background:#105b88}.secondary{color:var(--ink);background:#e8f2f6}.danger{color:#fff;background:var(--danger)}.hidden{display:none!important}.notice{margin:10px 0;padding:10px 12px;border-radius:10px;background:#eef6f9;color:#45667c;font-size:13px}.notice.error{background:#fff0f1;color:#9d303b}.notice.good{background:#e9f7f0;color:#176b4a}.join-code{font-size:38px;letter-spacing:.12em;font-weight:800;color:var(--blue);font-variant-numeric:tabular-nums}.url-box{display:flex;gap:8px}.url-box input{flex:1;min-width:0}.stat-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px}.stat{padding:14px;border-radius:12px;background:#eef6f9}.stat b{display:block;font-size:26px;line-height:1.1}.stat span{font-size:12px;color:var(--muted)}.activity{border:1px solid var(--line);border-radius:14px;padding:14px;margin:10px 0}.activity h3{margin:0 0 8px}.activity.active{border-color:#66b4d9;background:#f0f9fd}.list{list-style:none;padding:0;margin:8px 0;display:grid;gap:7px}.list li{display:flex;justify-content:space-between;gap:8px;padding:9px 10px;background:#f4f8fa;border-radius:9px;font-size:14px}.muted{color:var(--muted)}.student-shell{max-width:680px}.student-card{margin-top:26px}.student-name{font-weight:700}.big-button{display:block;width:min(340px,100%);min-height:105px;margin:20px auto;border:0;border-radius:24px;background:linear-gradient(145deg,#e9434d,#b91f32);color:#fff;font-size:32px;font-weight:800;box-shadow:0 12px 0 #891d29,0 17px 30px rgba(145,31,40,.24)}.big-button:active{transform:translateY(7px);box-shadow:0 5px 0 #891d29}.big-button:disabled{background:#a8b8c2;box-shadow:0 8px 0 #7f919c;cursor:not-allowed}.bullet-input{display:flex;gap:8px}.bullet-input input{flex:1;border:1px solid #bed3df;border-radius:11px;padding:12px}.message-wall{display:grid;gap:7px;margin-top:14px}.message{padding:9px 12px;background:#f2f8fb;border-radius:11px}.message b{font-size:13px;margin-right:6px}.qr-placeholder{display:grid;place-items:center;min-height:128px;border:2px dashed #99c4d8;border-radius:14px;background:#f5fbfd;text-align:center;color:#52758a;font-size:13px;padding:12px}@media(max-width:720px){.grid{grid-template-columns:1fr}.wide{grid-column:auto}.stat-grid{grid-template-columns:1fr 1fr}.top{padding:21px 18px}.shell{padding:18px 13px 60px}}