body {
  font-family: sans-serif;
  text-align: center;
  background-color: #f9f9f9;
}

table {
  border-collapse: collapse;
  margin: 20px auto;
}

td {
  padding: 0;
  margin: 0;
}

img.cell {
  width: 40px;
  height: 40px;
  display: block;
  border: 1px solid #ccc;
}