@salsan/iscss/dist/index.js

isCss is a Node.js package, return true if input is a valid Cascading Style Sheets

"use strict";
const css = require('css');
module.exports = function isCSS(data) {
    const value = css.parse(data, { silent: true });
    if ((value.stylesheet.parsingErrors.length > 0) || (value.stylesheet.rules.length === 0)) {
        return false;
    }
    else {
        return true;
    }
};