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/postcss/lib/declaration.js

@@ -0,0 +1,24 @@
+'use strict'
+
+let Node = require('./node')
+
+class Declaration extends Node {
+  get variable() {
+    return this.prop.startsWith('--') || this.prop[0] === '$'
+  }
+
+  constructor(defaults) {
+    if (
+      defaults &&
+      typeof defaults.value !== 'undefined' &&
+      typeof defaults.value !== 'string'
+    ) {
+      defaults = { ...defaults, value: String(defaults.value) }
+    }
+    super(defaults)
+    this.type = 'decl'
+  }
+}
+
+module.exports = Declaration
+Declaration.default = Declaration