the finishing touches

Shuffling the g_sets array will ensure variety.
A global g_pick will start at 0 and increment after each round.
A new function go() will serve both at the start and on clicking the map for another go.

index.html
...
        <img id='map' src='map.png' onClick='go();'>
...
  <script>
    Shuffle(g_sets);
    go();
  </script>
</body>
</html>
go() in functions.js
function go() {
  g_letters=0;
  load_squares(g_sets[g_pick]);
  g_pick++;
  g_found=0;
  for (var id=0;id<100;id++) {
    var el=document.getElementById(id);
    el.style.backgroundColor='white';
  }
  highlight(0);
}
portrait mode

Simply add the following to the bottom of your styles.css:

@media (orientation:portrait) {
  #game {
    flex-direction:column;
  }
}