<html>
<head>
<style>
.diagonal-cell {
  position: relative;
}

.diagonal-cell::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  transform: rotate(-45deg);
  transform-origin: top left;
}

</style>

</head>
<body>
<table>
  <tr>
    <td class="diagonal-cell">Diagonal Text</td>
    <td>Normal Text</td>
  </tr>
  <tr>
    <td>Normal Text</td>
    <td class="diagonal-cell">Diagonal Text</td>
  </tr>
</table>
