...
    <img id='join' src='images/join.png'>
    <div id='buttons'>
      <div id='different'>
        <img id='red' src='images/red.png' onClick="button_click('red');">
        different
      </div>
      <div id='same'>
        <img id='green' src='images/green.png' onClick="button_click('green');">
        same
      </div>
    </div>
    <div id='finale'></div>
  </div>
  ...
#finale {
  margin-top:-19vmin;
  font-size:6vmin;
  visibility:hidden;
}
function finale() {
  var el=document.getElementById('finale');
  el.textContent='Your score: '+g_score+' out of '+g_n;
  Show('finale');
}