JSFiddle - React, Tailwind, and code Playground

HTML

<table style="width:600px;">
  <tr>
    <td class="topRow">header1</td>
    <td class="topRow">header2</td>
    <td class="topRow">header3</td>
  </tr>
  <tr>
    <td>something1</td>
    <td>something2</td>
    <td>something3</td>
  </tr>
</table>

CSS

table{
    border-spacing: 0px;
}
.topRow{
    border-bottom: 1px solid black; 
    width:50%;
}