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/borderTopStyle.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var isValid = require('./borderStyle').isValid;
+module.exports.isValid = isValid;
+
+module.exports.definition = {
+  set: function(v) {
+    if (isValid(v)) {
+      if (v.toLowerCase() === 'none') {
+        v = '';
+        this.removeProperty('border-top-width');
+      }
+      this._setProperty('border-top-style', v);
+    }
+  },
+  get: function() {
+    return this.getPropertyValue('border-top-style');
+  },
+  enumerable: true,
+  configurable: true,
+};