<table>
  <tr>
    <td>Колонка 1</td>
    <td>Колонка 2</td>
    <td>Колонка 3</td>
  </tr>
  <tr>
    <td>1</td>
    <td>2</td>
    <td>3</td>
  </tr>
  <tr>
    <td>4</td>
    <td>5</td>
    <td>6</td>
  </tr>
  <tr>
    <td>7</td>
    <td>8</td>
    <td>9</td>
  </tr>
</table>

table {
  border-collapse: collapse;
}

td {
  border: 1px solid red;
  border-top: none;
  border-left: none;
  padding: 5px;
}

tr:last-child td {
  border-bottom: none;
  border-color: transparent;
  background: linear-gradient(red, red) no-repeat border-box 0 0 / 1px 50%;
}

tr:first-child td {
  border-right: transparent;
  background: linear-gradient(red, red) no-repeat border-box 0 100% / 1px 50%;
}

tr:last-child td:first-child,
tr:first-child td:first-child {
  background: none;
}

td:last-child {
  border-right: none;
}