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-browser-comments/README.md

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+# PostCSS Browser Comments [<img src="https://postcss.github.io/postcss/logo.svg" alt="PostCSS" width="90" height="90" align="right">][postcss]
+
+[![NPM Version][npm-img]][npm-url]
+[![Build Status][cli-img]][cli-url]
+[![Support Chat][git-img]][git-url]
+
+[PostCSS Browser Comments] lets you keep only the CSS you need based on
+comments and your [browserslist].
+
+```css
+/**
+ * Prevent adjustments of font size after orientation changes in IE and iOS.
+ */
+
+html {
+  -ms-text-size-adjust: 100%;
+  -webkit-text-size-adjust: 100%;
+}
+```
+
+The comment and rule above would be removed with the following browserslist:
+
+```yml
+last 2 chrome versions
+```
+
+The rule below would be more carefully altered:
+
+```css
+/**
+ * 1. Add the correct box sizing in Firefox.
+ * 2. Show the overflow in Edge and IE.
+ */
+
+hr {
+  box-sizing: content-box; /* 1 */
+  height: 0; /* 1 */
+  overflow: visible; /* 2 */
+}
+
+/* with a `last 2 firefox versions` browserslist becomes */
+
+/**
+ * 1. Add the correct box sizing in Firefox.
+ * 2. Show the overflow in Edge and IE.
+ */
+
+hr {
+  box-sizing: content-box; /* 1 */
+  height: 0; /* 1 */
+}
+```
+
+---
+
+[PostCSS Browser Comments] can remove rules based upon the comment above them,
+or it can remove declarations using numbered comments that reference the rule
+above them. In the later case, when all of the numbered comments are removed,
+then the entire rule and comment are also removed.
+
+## Usage
+
+Add [PostCSS Browser Comments] to your project:
+
+```bash
+npm install postcss postcss-browser-comments --save-dev
+```
+
+Use [PostCSS Browser Comments] to process your CSS:
+
+```js
+const postcssBrowserComments = require('postcss-browser-comments');
+
+postcssBrowserComments.process(YOUR_CSS /*, processOptions, pluginOptions */);
+```
+
+Or use it as a [PostCSS] plugin:
+
+```js
+const postcss = require('postcss');
+const postcssBrowserComments = require('postcss-browser-comments');
+
+postcss([
+  postcssBrowserComments(/* pluginOptions */)
+]).process(YOUR_CSS /*, processOptions */);
+```
+
+[PostCSS Browser Comments] runs in all Node environments, with special instructions for:
+
+| [Node](INSTALL.md#node) | [PostCSS CLI](INSTALL.md#postcss-cli) | [Webpack](INSTALL.md#webpack) | [Create React App](INSTALL.md#create-react-app) | [Gulp](INSTALL.md#gulp) | [Grunt](INSTALL.md#grunt) |
+| --- | --- | --- | --- | --- | --- |
+
+## Options
+
+### browsers
+
+The `browsers` option overrides of the project’s browserslist.
+
+```js
+postcssBrowserComments({
+  browsers: 'last 2 versions'
+});
+```
+
+[cli-img]: https://img.shields.io/travis/csstools/postcss-browser-comments/main.svg
+[cli-url]: https://travis-ci.org/csstools/postcss-browser-comments
+[git-img]: https://img.shields.io/badge/support-chat-blue.svg
+[git-url]: https://gitter.im/postcss/postcss
+[npm-img]: https://img.shields.io/npm/v/postcss-browser-comments.svg
+[npm-url]: https://www.npmjs.com/package/postcss-browser-comments
+
+[browserslist]: https://github.com/browserslist/browserslist
+[PostCSS]: https://github.com/postcss/postcss
+[PostCSS Browser Comments]: https://github.com/csstools/postcss-browser-comments