JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outer">
    <div class="c1">
        c1 should be black
    </div>
    <div class="c2">
        c2 should be black
    </div>
    <div class="c3">
        c3 should be black
    </div>
</div>
<div id="somethingelse">
    <div class="c1">
       c1 should be red
    </div>
    <div class="c2">
        c2 should be red
    </div>
    <div class="c3">
        c3 should be red
    </div>
</div>

CSS

:not(#outer) .c1 {
    color: #ff0000;
}

div:not(#outer) .c2 {
    color: #ff0000;
}

:not(#outer) > .c3 {
    color: #ff0000;
}