Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/cssom/lib/CSSDocumentRule.js

@@ -0,0 +1,39 @@
+//.CommonJS
+var CSSOM = {
+    CSSRule: require("./CSSRule").CSSRule,
+    MatcherList: require("./MatcherList").MatcherList
+};
+///CommonJS
+
+
+/**
+ * @constructor
+ * @see https://developer.mozilla.org/en/CSS/@-moz-document
+ */
+CSSOM.CSSDocumentRule = function CSSDocumentRule() {
+    CSSOM.CSSRule.call(this);
+    this.matcher = new CSSOM.MatcherList();
+    this.cssRules = [];
+};
+
+CSSOM.CSSDocumentRule.prototype = new CSSOM.CSSRule();
+CSSOM.CSSDocumentRule.prototype.constructor = CSSOM.CSSDocumentRule;
+CSSOM.CSSDocumentRule.prototype.type = 10;
+//FIXME
+//CSSOM.CSSDocumentRule.prototype.insertRule = CSSStyleSheet.prototype.insertRule;
+//CSSOM.CSSDocumentRule.prototype.deleteRule = CSSStyleSheet.prototype.deleteRule;
+
+Object.defineProperty(CSSOM.CSSDocumentRule.prototype, "cssText", {
+  get: function() {
+    var cssTexts = [];
+    for (var i=0, length=this.cssRules.length; i < length; i++) {
+        cssTexts.push(this.cssRules[i].cssText);
+    }
+    return "@-moz-document " + this.matcher.matcherText + " {" + cssTexts.join("") + "}";
+  }
+});
+
+
+//.CommonJS
+exports.CSSDocumentRule = CSSOM.CSSDocumentRule;
+///CommonJS