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/cssstyle/lib/properties/backgroundAttachment.js

@@ -0,0 +1,24 @@
+'use strict';
+
+var parsers = require('../parsers');
+
+var isValid = (module.exports.isValid = function isValid(v) {
+  return (
+    parsers.valueType(v) === parsers.TYPES.KEYWORD &&
+    (v.toLowerCase() === 'scroll' || v.toLowerCase() === 'fixed' || v.toLowerCase() === 'inherit')
+  );
+});
+
+module.exports.definition = {
+  set: function(v) {
+    if (!isValid(v)) {
+      return;
+    }
+    this._setProperty('background-attachment', v);
+  },
+  get: function() {
+    return this.getPropertyValue('background-attachment');
+  },
+  enumerable: true,
+  configurable: true,
+};