tidied up your code a bit (mainly by running through jshint and fixing issues, also got rid of dodgy new function() constructor, used more standardized approach

[jonathan-annett]

/**
 * CSS-JSON Converter for JavaScript
 * Converts CSS to JSON and back.
 * Version 2.1
 *
 * Released under the MIT license.
 *
 * Copyright (c) 2013 Aram Kocharyan, http://aramk.com/

 Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
 documentation files (the "Software"), to deal in the Software without restriction, including without limitation
 the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and
 to permit persons to whom the Software is furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in all copies or substantial portions
 of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
 THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 */


/*******************************************************************************
 *  UMD pattern for exporting module
 */
(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD. Register as an anonymous module.
        define([], factory);
    } else if (typeof exports === 'object') {
        // Node. Does not work with strict CommonJS, but
        // only CommonJS-like environments that support module.exports,
        // like Node.
        module.exports = factory();
    } else {
        // Browser globals (root is window)
        root.CSSJSON = factory();
  }
}(this, function () {

    var CSSJSON = function () {

        var base = {};

        if (typeof String.prototype.trim !== 'function') {
            String.prototype.trim = function () {
                return this.replace(/^\s+|\s+$/g, '');
            };
        }

        if (typeof String.prototype.repeat !== 'function') {
            String.prototype.repeat = function (n) {
                return new Array(1 + n).join(this);
            };
        }
/*
        var selX = /([^\s\;\{\}][^\;\{\}]*)\{/g;
        var endX = /\}/g;
        var lineX = /([^\;\{\}]*)\;/g;
*/        
        var commentX = /\/\*[\s\S]*?\*\//g;
        var lineAttrX = /([^\:]+):([^\;]*);/;

        // This is used, a concatenation of all above. We use alternation to
        // capture.
        var altX = /(\/\*[\s\S]*?\*\/)|([^\s\;\{\}][^\;\{\}]*(?=\{))|(\})|([^\;\{\}]+\;(?!\s*\*\/))/gmi;

        // Capture groups
        var capComment = 1;
        var capSelector = 2;
        var capEnd = 3;
        var capAttr = 4;

        var isEmpty = function (x) {
            return typeof x === 'undefined' || x.length === 0 || x === null;
        };

        /**
         * Input is css string and current pos, returns JSON object
         *
         * @param cssString
         *            The CSS string.
         * @param args
         *            An optional argument object. ordered: Whether order of
         *            comments and other nodes should be kept in the output. This
         *            will return an object where all the keys are numbers and the
         *            values are objects containing "name" and "value" keys for each
         *            node. comments: Whether to capture comments. split: Whether to
         *            split each comma separated list of selectors.
         */
        base.toJSON = function (cssString, args) {
            var node = {
                children: {},
                attributes: {}
            };
            var match = null;
            var count = 0;

            if (typeof args == 'undefined') {
                args = {
                    ordered: false,
                    comments: false,
                    stripComments: false,
                    split: false
                };
            }
            if (args.stripComments) {
                args.comments = false;
                cssString = cssString.replace(commentX, '');
            }


            var i,bits,sel,att,name,newNode;


            while ((match = altX.exec(cssString)) !== null) {
                if (!isEmpty(match[capComment]) && args.comments) {
                    // Comment
                    var add = match[capComment].trim();
                    node[count++] = add;
                } else if (!isEmpty(match[capSelector])) {
                    // New node, we recurse
                        name = match[capSelector].trim();
                    // This will return when we encounter a closing brace
                        newNode = base.toJSON(cssString, args);
                    if (args.ordered) {
                        // Since we must use key as index to keep order and not
                        // name, this will differentiate between a Rule Node and an
                        // Attribute, since both contain a name and value pair.
                        node[count++] = { name : name, value:newNode, type:'rule'};
                    } else {
                        if (args.split) {
                            bits = name.split(',');
                        } else {
                            bits = [name];
                        }
                        for (i in bits) {
                            sel = bits[i].trim();
                            if (sel in node.children) {
                                for (att in newNode.attributes) {
                                    node.children[sel].attributes[att] = newNode.attributes[att];
                                }
                            } else {
                                node.children[sel] = newNode;
                            }
                        }
                    }
                } else if (!isEmpty(match[capEnd])) {
                    // Node has finished
                    return node;
                } else if (!isEmpty(match[capAttr])) {
                    var value,
                        line = match[capAttr].trim(),
                        attr = lineAttrX.exec(line);
                    if (attr) {
                        // Attribute
                        name = attr[1].trim();
                        value = attr[2].trim();
                        if (args.ordered) {
                            node[count++] = {name:name,value:value,type:'attr'};
                        } else {
                            if (name in node.attributes) {
                                var currVal = node.attributes[name];
                                if (!(currVal instanceof Array)) {
                                    node.attributes[name] = [currVal];
                                }
                                node.attributes[name].push(value);
                            } else {
                                node.attributes[name] = value;
                            }
                        }
                    } else {
                        // Semicolon terminated line
                        node[count++] = line;
                    }
                }
            }

            return node;
        };

        /**
         * @param node
         *            A JSON node.
         * @param depth
         *            The depth of the current node; used for indentation and
         *            optional.
         * @param breaks
         *            Whether to add line breaks in the output.
         */
        base.toCSS = function (node, depth, breaks) {
            var i,att,first,cssString = '';
            if (typeof depth == 'undefined') {
                depth = 0;
            }
            if (typeof breaks == 'undefined') {
                breaks = false;
            }
            if (node.attributes) {
                for (i in node.attributes) {
                    att = node.attributes[i];
                    if (att instanceof Array) {
                        for (var j = 0; j < att.length; j++) {
                            cssString += strAttr(i, att[j], depth);
                        }
                    } else {
                        cssString += strAttr(i, att, depth);
                    }
                }
            }
            if (node.children) {
                first = true;
                for (i in node.children) {
                    if (breaks && !first) {
                        cssString += '\n';
                    } else {
                        first = false;
                    }
                    cssString += strNode(i, node.children[i], depth);
                }
            }
            return cssString;
        };

        // Helpers

        var strAttr = function (name, value, depth) {
            return '\t'.repeat(depth) + name + ': ' + value + ';\n';
        };

        var strNode = function (name, value, depth) {
            var cssString = '\t'.repeat(depth) + name + ' {\n';
            cssString += base.toCSS(value, depth + 1);
            cssString += '\t'.repeat(depth) + '}\n';
            return cssString;
        };

        return base;
    };

    return CSSJSON();
}));

[jonathan-annett]

sorry should have mentioned - this is a tidy up of the version that's exported to npm (might not be the one thats on github here)

[DogAndHerDude]

Saddly you didn't seem to test your changes, as it currently outputs bad CSS from a valid JSON.

const css = { children: { '.lumi-calc': { .children: { '.lumi-calc-title': { attributes: { 'border-width': '2px' } } } } } }

gets parsed into:

.lumi-calc { .lumi-calc-title { border-radius: 0px; } }

That might be valid SCSS or LESS, but not CSS.