JSFiddle - React, Tailwind, and code Playground

HTML

<table>
  <tr>
    <td style="text-align: center; background-color: #1b6d85; color: white;">Tage:</td>
    <td style="text-align: center; background-color: #1b6d85; color: white;">##</td>
    <td style="background-color: black;"></td>
    <td style="text-align: center; background-color: #1b6d85; color: white;" colspan="5">xx</td>
    <td style="background-color: black;"></td>
    <td style="text-align: center; background-color: #1b6d85; color: white;" colspan="4">xxxx</td>
    <td style="background-color: black;"></td>
    <td style="text-align: center; background-color: #1b6d85; color: white;" colspan="4">xxxxxx</td>
    <td style="background-color: black;"></td>
    <td style="text-align: center; background-color: #1b6d85; color: white;" colspan="4">xxxx</td>
    <td style="background-color: black;"></td>
    <td style="text-align: center; background-color: #1b6d85; color: white;">Monat:</td>
    <td style="text-align: center; background-color: #1b6d85; color: white;">***</td>
  </tr>
  <tr>
    <th class="header-label"><span>xxx</span></th>
    <th class="header-label"><span>xxxx.</span></th>
    <th style="background-color: black;"></th>
    <th class="header-label"><span>xxxxx</span></th>
    <th class="header-label"><span>xxxxx</span></th>
    <th class="header-label"><span>xxxxxx</span></th>
    <th class="header-label"><span>xxxxxx</span></th>
    <th class="header-label"><span>xxxxxx</span></th>
    <th style="background-color: black;"></th>
    <th class="header-label"><span>xxx</span></th>
    <th class="header-label"><span>xxxx</span></th>
    <th class="header-label"><span>xxxxx</span></th>
    <th class="header-label"><span>xxxxxx</span></th>
    <th style="background-color: black;"></th>
    <th class="header-label"><span>x</span></th>
    <th class="header-label"><span>xxxxxxxx</span></th>
    <th class="header-label"><span>x</span></th>
    <th class="header-label"><span>xxxxxxxx</span></th>
    <th style="background-color: black;"></th>
    <th...

CSS

.header-label span {
  writing-mode: sideways-rl;
}