body {
    font-family: "Segoe UI", sans-serif;
      background: #f7f7f7;
      margin: 0;
      height: 100%;
     
}
header {
    background-color: #005b96;
    color: white;
    text-align: center;
    padding: 15px;
}
nav a {
    color: white;
    margin: 0 10px;
    text-decoration: none;
    font-weight: bold;
}
nav a.active, nav a:hover {
    text-decoration: underline;
}
main {
    background-color: white;
    margin: 20px;
}
footer {
    text-align: center;
    background-color: #005b96;
    color: white;
    padding: 10px;
    position: fixed;
    bottom: 0;
    width: 100%;
}
.form-container {
    background: #fff;
    padding: 30px 40px;
    border-radius: 12px;
    box-shadow: 0 3px 10px rgba(0,0,0,0.15);
    width: 380px;
    text-align: center;
  }

  h2 {
    color: #0a6ebd;
    margin-bottom: 20px;
  }

  form {
    display: flex;
    flex-direction: column;
    gap: 12px;
  }

  input, select {
    padding: 10px;
    border-radius: 8px;
    border: 1px solid #ccc;
    font-size: 15px;
  }

  input:focus, select:focus {
    outline: none;
    border-color: #0a6ebd;
    box-shadow: 0 0 5px rgba(10,110,189,0.3);
  }

  button {
    background: #0a6ebd;
    color: white;
    border: none;
    padding: 10px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 16px;
    transition: background 0.3s;
  }

  button:hover {
    background: #09579c;
  }

  .back-link {
    display: inline-block;
    margin-top: 10px;
    text-decoration: none;
    color: #0a6ebd;
    font-size: 14px;
  }
  .back-link:hover {
    text-decoration: underline;
  }

  /* Nút menu */
  .menu-toggle {
    font-size: 22px;
    background: #0a6ebd;
    color: white;
    padding: 10px 15px;
    margin: 15px;
    border-radius: 8px;
    display: inline-block;
    cursor: pointer;
    transition: background 0.3s;
  }
  .menu-toggle:hover {
    background: #095ba0;
  }
  
  /* Menu ẩn */
  #menu-sach {
    max-width: 300px;
    background: white;
    border-radius: 10px;
    padding: 15px;
    margin: 15px;
    box-shadow: 0 2px 8px rgba(0,0,0,0.15);
    transform: scaleY(0);
    transform-origin: top;
    transition: transform 0.3s ease;
    overflow: hidden;
  }
  #menu-sach.menu-show {
    transform: scaleY(1);
  }
  
  /* Danh sách sách */
  #menu-sach h3 {
    color: #0a6ebd;
    border-bottom: 2px solid #0a6ebd;
    padding-bottom: 5px;
  }
  
  #menu-sach ul {
    list-style: none;
    padding-left: 10px;
  }
  
  #menu-sach li {
    padding: 6px 0;
    font-size: 16px;
    color: #333;
    transition: color 0.2s;
  }
  #menu-sach li:hover {
    color: #0a6ebd;
    cursor: pointer;
  }