JSFiddle - React, Tailwind, and code Playground

JavaScript

function normalizeSelectors(aSelector) {

    var parser   = new DOMParser(),
        string   = '<style>' + aSelector + '{}</style>',
        doc      = parser.parseFromString(string, "text/html"),
        cssRules = doc.querySelector('style').sheet.cssRules;
    
        if (cssRules[0]) {
            return cssRules[0].selectorText
        } else {
            // selector is invalid...
        }
}

console.log(normalizeSelectors('foo     bar'))