#guesstable {
  cell-spacing: 0;
  border-collapse: collapse;
  border: 1px solid black;
}
#guesstable tr:first-child {
  vertical-align: bottom;
  border-bottom: 1px solid black;
}
#guesstable th, #guesstable td { text-align: center; }
#guesstable th:first-child + th + th + th,
#guesstable td:first-child + td + td + td,
#guesstable th:first-child + th + th + th + th + th + th,
#guesstable td:first-child + td + td + td + td + td + td {
  border-left: 1px solid black;
}