JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <thead>
        <th class="sortup">A</th> <!-- Draw an arrow via CSS? -->
        <th class="sortdown">B</th>
        <th>C</th>
    </thead>
    <tr>
        <td></td>
        <td></td>
        <td></td>        
    </tr>  
</table>

CSS

.sortup:after {
      content:"\25BC";
      float:right;
      margin-left:1em;
    }
    .sortdown:after {
      content:"\25B2";
      float:right;
      margin-left:1em;
    }

th {border:1px solid #ccc;padding:.5em}