button_help:hover {
  cursor: pointer;
  background-color: #00000077;
}

@media print {
  #button_help {
    display: none;
  }

  div.hint {
    display: none;
  }
}

    </style>
  </head>
  <body>
    <button id="button_help">?</button>
    <div id="hints" class="hint" style="display: none">
      <button id="close-hints">x</button>
      <span id="hint-text"></span>
      <ul>
        <li><b>Hover</b> - highlight</li>
        <li><b>Right-click</b> - pin highlight</li>
        <li><b>ESC</b> - clear</li