JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.sortup:before {
    content:'';
    display:inline-block;
    border-style: solid;
    border-width: 0 8px 10px 8px;
    border-color: transparent transparent #007bff transparent;
}
.sortup:after {
    content:'';
    display:inline-block;
    border-style: solid;
    border-width: 10px 8px 0 8px;
    border-color: #007bff transparent transparent transparent;
}