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/autoprefixer/lib/hacks/fullscreen.js

@@ -0,0 +1,20 @@
+let Selector = require('../selector')
+
+class Fullscreen extends Selector {
+  /**
+   * Return different selectors depend on prefix
+   */
+  prefixed(prefix) {
+    if (prefix === '-webkit-') {
+      return ':-webkit-full-screen'
+    }
+    if (prefix === '-moz-') {
+      return ':-moz-full-screen'
+    }
+    return `:${prefix}fullscreen`
+  }
+}
+
+Fullscreen.names = [':fullscreen']
+
+module.exports = Fullscreen