JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="red">Red</div>
    <div class="red">Red</div>
    <div class="red">Red</div>
    
    <div class="black">Black</div>
    <div class="black">Black</div>
    <div class="black">Black</div>

    <div class="green">Green</div>
    <div class="green">Green</div>
    <div class="green">Green</div>
</div>

CSS

.red {
    color:red;
}
.black {
    color:black;
}
.green {
    color:green;
}

div.black:first-child,
div:not(.black) + div.black {
    font-weight: bold;
}