JSFiddle - React, Tailwind, and code Playground

HTML

<table class="OpenCourse">
    <tr>
        <td>foo</td>
    </tr>
    <tr>
        <td>bar</td>
    </tr>
</table>

<table class="OpenCourse">
    <tr>
        <td>foo</td>
    </tr>
    <tr>
        <td>bar</td>
    </tr>
</table>

CSS

.OpenCoursesHeader { background-color:gray; }

JavaScript

$(function() {
    $(".OpenCourse").find("tr:first").addClass("OpenCoursesHeader");
});