JSFiddle - React, Tailwind, and code Playground

HTML

<div class="element1">
    <div class="element2"></div>
</div>

CSS

.element1 {
    background-color:yellow;
    min-height:80px;
}

.element2 {
    background-color:purple;
    min-height:80px;
    /*margin:0 auto; center element within it's container*/
}

JavaScript

$(function() {
    var calc = 0;
    calc = $(".element1").width() - 100;
    $(".element2").css({"width" : calc + "px"}); 
});