:root{--bg:#fffffe;--surface:#fffffe;--surface-muted:#eefbf8;--text:#00214d;--paragraph:#1b2d45;--muted:#536377;--line:#00214d;--primary:#00ebc7;--primary-dark:#00d3b3;--accent:#fde24f;--secondary:#ff5470;--danger:#b3263e;--success:#008f7a;--shadow:0 8px 0 rgba(0,33,77,.08)}*{box-sizing:border-box}body,html{min-height:100%}body{margin:0;background:var(--bg);color:var(--paragraph);font-family:Arial,Helvetica,sans-serif;letter-spacing:0}button,input,select,textarea{font:inherit}button{align-items:center;border:2px solid var(--line);border-radius:6px;cursor:pointer;display:inline-flex;font-weight:700;gap:8px;justify-content:center;min-height:40px;padding:0 14px}button:disabled{cursor:not-allowed;opacity:.55}input,select,textarea{background:#fff;border:1px solid var(--line);border-radius:6px;color:var(--text);min-height:42px;padding:10px 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(max-width:520px){.actions,.link-button,.nav,.nav a,button{width:100%}.nav{display:grid;grid-template-columns:1fr}.topbar{gap:12px}.mode-switch{grid-template-columns:1fr}.brand{align-items:flex-start;flex-direction:column;gap:2px}.login-panel,.panel{border-width:2px;padding:14px}.lesson h1{font-size:22px}.metric strong{font-size:24px}}