index.html
<html>
<head>
  <title>Jigsaw</title>
  <link rel='stylesheet' href='styles.css'>
  <script src='library.js'></script>
  <script src='globals.js'></script>
  <script src='pieces.js'></script>
  <script src='scramble.js'></script>
  <script src='piece_clicked.js'></script>
  <script src='finished.js'></script>
  <script src='finale.js'></script>
</head>
<body>
  <div id='grid'>
    <img src='images/1.jpg' id='pic'>
    <script>pieces(); scramble();</script>
  </div>
</body>
</html>
styles.css
body {
  background-color: black;
}
#grid {
  margin:10px auto;
...
#pic {
  grid-row: 1/ span 5;
  grid-column: 1/ span 6;
  visibility: hidden;
}
finale.js
function finale() {
  var el=document.getElementById('pic');
  Show('pic');
  Hide_class('piece');
}