JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li class="class1">A</li>
    <li class="class1 class2 some other classes">B</li>
    <li class="class1">C</li>
</ul>
<ul>
    <li class="class1 class2 some other classes">D</li>
    <li class="class1">E</li>
    <li class="class1">F</li>
</ul>

CSS

li[class=class1]:first-child {
    background-color: red;
}