* { box-sizing: border-box; }
    body {
      margin: 0;
      font-family: 'Segoe UI', sans-serif;
      color: #1f2937;
      background: #eef2f7;
    }
    main {
      width: min(920px, calc(100% - 32px));
      margin: 32px auto;
      background: #fff;
      border: 1px solid #d8e0ea;
      border-radius: 8px;
      box-shadow: 0 10px 30px rgba(15, 23, 42, 0.08);
      overflow: hidden;
    }
    header {
      display: flex;
      justify-content: space-between;
      gap: 16px;
      padding: 24px 28px;
      border-bottom: 1px solid #e5e7eb;
      background: #f8fafc;
    }
    h1 { margin: 0; font-size: 24px; }
    .role { color: #64748b; font-size: 14px; margin-top: 6px; }
    .back {
      align-self: center;
      color: #2563eb;
      text-decoration: none;
      font-weight: 600;
      font-size: 14px;
    }
    form { padding: 28px; }
    section { margin-bottom: 28px; }
    h2 {
      margin: 0 0 16px;
      font-size: 16px;
      color: #334155;
      border-bottom: 1px solid #e5e7eb;
      padding-bottom: 8px;
    }
    .grid {
      display: grid;
      grid-template-columns: repeat(2, minmax(0, 1fr));
      gap: 16px;
    }
    label {
      display: block;
      font-size: 13px;
      font-weight: 700;
      color: #475569;
      margin-bottom: 6px;
    }
    input {
      width: 100%;
      height: 42px;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      padding: 0 12px;
      font-size: 14px;
      outline: none;
      background: #fff;
    }
    input:focus { border-color: #2563eb; box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.12); }
    input[readonly] { color: #64748b; background: #f8fafc; }
    .toggle-row {
      display: flex;
      align-items: center;
      gap: 10px;
      margin-bottom: 14px;
      font-size: 14px;
      color: #334155;
    }
    .toggle-row input { width: 18px; height: 18px; }
    .password-fields[hidden],
    .student-section[hidden],
    .modal[hidden] { display: none; }
    .oauth-grid {
      display: grid;
      grid-template-columns: repeat(3, minmax(0, 1fr));
      gap: 12px;
    }
    .oauth-card {
      border: 1px solid #d8e0ea;
      border-radius: 8px;
      padding: 14px;
      background: #f8fafc;
    }
    .oauth-card strong { display: block; margin-bottom: 8px; }
    .oauth-badge {
      display: inline-block;
      margin-bottom: 12px;
      padding: 3px 8px;
      border-radius: 999px;
      font-size: 12px;
      font-weight: 700;
      background: #e2e8f0;
      color: #334155;
    }
    .oauth-badge.connected { background: #dcfce7; color: #166534; }
    .oauth-card button { width: 100%; min-height: 36px; }
    .oauth-card button[disabled] { cursor: not-allowed; opacity: 0.55; }
    .actions {
      display: flex;
      justify-content: space-between;
      gap: 12px;
      border-top: 1px solid #e5e7eb;
      padding-top: 20px;
    }
    button {
      min-height: 42px;
      border: 0;
      border-radius: 6px;
      padding: 0 18px;
      font-weight: 700;
      cursor: pointer;
    }
    .primary { background: #2563eb; color: white; }
    .danger { background: #dc2626; color: white; }
    .secondary { background: #e2e8f0; color: #334155; }
    .message {
      min-height: 20px;
      margin: 0 28px 24px;
      font-size: 14px;
    }
    .message.ok { color: #15803d; }
    .message.error { color: #dc2626; }
    .modal {
      position: fixed;
      inset: 0;
      display: grid;
      place-items: center;
      padding: 20px;
      background: rgba(15, 23, 42, 0.5);
    }
    .modal-panel {
      width: min(420px, 100%);
      background: #fff;
      border-radius: 8px;
      padding: 24px;
      box-shadow: 0 20px 60px rgba(15, 23, 42, 0.25);
    }
    .modal-panel h2 { margin-bottom: 10px; }
    .modal-panel p { color: #64748b; line-height: 1.5; }
    .modal-actions {
      display: flex;
      justify-content: flex-end;
      gap: 10px;
      margin-top: 18px;
    }
    @media (max-width: 680px) {
      header, .actions { flex-direction: column; }
      .grid { grid-template-columns: 1fr; }
      main { margin: 16px auto; width: calc(100% - 20px); }
      form, header { padding: 20px; }
    }