JSFiddle - React, Tailwind, and code Playground

HTML

<style id="the-style">
    #rule1 { color:red }
    #rule2 { color:green }
    #rule2 em { color:lime }
    #rule3 { color:blue }
</style>

<p id="rule1">Rule 1</p>
<p id="rule2">Rule <em>2!!</em></p>
<p id="rule3">Rule 3</p>

JavaScript

var styleTag = document.getElementById ("the-style");
var sheet = styleTag.sheet ? styleTag.sheet : styleTag.styleSheet;

if (sheet.cssRules) { // all browsers, except IE before version 9
    for (var i=0; i<sheet.cssRules.length; i++) {
        if (sheet.cssRules[i].selectorText === '#rule2 em') {        
            // console.log(sheet.cssRules[i]);
            sheet.deleteRule (i);
        }
    }  
}
else 
{  // Internet Explorer before version 9
    for (var i=0; i<sheet.rules.length; i++) {
        if (sheet.rules[i].selectorText === '#rule2 em') {       
           // console.log(sheet.cssRules[i]);
            sheet.removeRule (i);
        }
    } 
}