*{box-sizing:border-box;margin:0;padding:0}
  :root{--bg:#f4f6f9;--card:#fff;--primary:#4a90e2;--primary-soft:#e8f1fc;--text:#2c3e50;--text-sub:#7b8a99;--border:#eef1f5;--shadow:0 2px 12px rgba(0,0,0,.06);--radius:16px}
  body{font-family:-apple-system,BlinkMacSystemFont,"PingFang SC","Microsoft YaHei",sans-serif;background:var(--bg);color:var(--text);min-height:100vh;padding:24px}
  .app{max-width:1440px;margin:0 auto}
  .card{background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);padding:26px}
  .header{display:flex;align-items:center;justify-content:space-between;margin-bottom:22px}
  .header h1{font-size:22px;font-weight:600}
  .back{font-size:13px;color:var(--text-sub);text-decoration:none;padding:6px 12px;background:var(--bg);border-radius:8px}
  .back:hover{background:var(--primary-soft);color:var(--primary)}
  label{display:block;font-size:13px;color:var(--text-sub);margin-bottom:6px}
  .row{display:flex;gap:10px;align-items:center;margin-bottom:16px}
  .row input{flex:1;padding:11px 12px;border:1px solid var(--border);border-radius:10px;font-size:14px}
  .row span{color:var(--text-sub);font-size:13px}
  input:focus{outline:none;border-color:var(--primary)}
  .result-box{background:linear-gradient(135deg,var(--primary),#6aa9e9);border-radius:14px;padding:20px;color:#fff;text-align:center;margin-top:8px}
  .result-box .bmi{font-size:42px;font-weight:700}
  .result-box .level{font-size:15px;margin-top:6px;opacity:.9}
  .bar{height:10px;background:#fff3;border-radius:5px;margin-top:14px;position:relative;overflow:hidden}
  .bar .fill{height:100%;background:#fff;width:0%;border-radius:5px;transition:width .4s}
  .tip{margin-top:14px;font-size:13px;color:var(--text-sub);line-height:1.7}
  .tip b{color:var(--text)}