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/@csstools/postcss-trigonometric-functions/README.md

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+# PostCSS Trigonometric Functions [<img src="https://postcss.github.io/postcss/logo.svg" alt="PostCSS Logo" width="90" height="90" align="right">][postcss]
+
+[<img alt="npm version" src="https://img.shields.io/npm/v/@csstools/postcss-trigonometric-functions.svg" height="20">][npm-url] [<img alt="CSS Standard Status" src="https://cssdb.org/images/badges/trigonometric-functions.svg" height="20">][css-url] [<img alt="Build Status" src="https://github.com/csstools/postcss-plugins/workflows/test/badge.svg" height="20">][cli-url] [<img alt="Discord" src="https://shields.io/badge/Discord-5865F2?logo=discord&logoColor=white">][discord]
+
+[PostCSS Trigonometric Functions] lets you use `sin`, `cos`, `tan`, `asin`, `acos`, `atan` and `atan2` to be able to compute trigonometric relationships following the [CSS Values 4] specification.
+
+```pcss
+.trigonometry {
+	line-height: sin(pi / 4);
+	line-height: cos(.125turn);
+	line-height: tan(50grad);
+	transform: rotate(asin(-1));
+	transform: rotate(asin(sin(30deg + 1.0471967rad)));
+	transform: rotate(acos(-1));
+	transform: rotate(acos(cos(0 / 2 + 1 - 1)));
+	transform: rotate(atan(infinity));
+	transform: rotate(atan(e - 2.7182818284590452354));
+	transform: rotate(atan2(-infinity,-infinity));
+	transform: rotate(atan2(-infinity,infinity));
+	transform: rotate(atan2(-infinity,infinity));
+	transform: rotate(atan2(90, 15));
+}
+
+/* becomes */
+
+.trigonometry {
+	line-height: 0.70711;
+	line-height: 0.70711;
+	line-height: 1;
+	transform: rotate(-90deg);
+	transform: rotate(90deg);
+	transform: rotate(180deg);
+	transform: rotate(0deg);
+	transform: rotate(90deg);
+	transform: rotate(0deg);
+	transform: rotate(-135deg);
+	transform: rotate(-45deg);
+	transform: rotate(-45deg);
+	transform: rotate(80.54deg);
+}
+```
+
+## Usage
+
+Add [PostCSS Trigonometric Functions] to your project:
+
+```bash
+npm install postcss @csstools/postcss-trigonometric-functions --save-dev
+```
+
+Use it as a [PostCSS] plugin:
+
+```js
+const postcss = require('postcss');
+const postcssTrigonometricFunctions = require('@csstools/postcss-trigonometric-functions');
+
+postcss([
+	postcssTrigonometricFunctions(/* pluginOptions */)
+]).process(YOUR_CSS /*, processOptions */);
+```
+
+[PostCSS Trigonometric Functions] 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) |
+| --- | --- | --- | --- | --- | --- |
+
+## ⚠️ About custom properties
+
+Given the dynamic nature of custom properties it's impossible to know what the variable value is, which means the plugin can't compute a final value for the stylesheet.
+
+Because of that, any usage that contains a `var` is skipped.
+
+## Units
+
+[PostCSS Trigonometric Functions] lets you use different special units that are within the spec and computed at run time to be able to calculate the result of the trigonometric function.
+
+The following units are supported:
+
+* `pi`: Computes to `Math.PI` which is `3.141592653589793`
+* `e`: Computes to `Math.E` which is `2.718281828459045`
+* `infinity`, `-infinity`: Compute to `Infinity` and `-Infinity` respectively. Note that the usage is case insensitive so `InFiNiTy` is a valid value.
+
+Some calculations (such as `sin(-infinity)`) might return `NaN` as per the spec. Given that `NaN` can't be replaced with a value that's useful to CSS it is left as is, as the result will be effectively ignored by the browser.
+
+## Options
+
+### preserve
+
+The `preserve` option determines whether the original notation
+is preserved. By default, it is not preserved.
+
+```js
+postcssTrigonometricFunctions({ preserve: true })
+```
+
+```pcss
+.trigonometry {
+	line-height: sin(pi / 4);
+	line-height: cos(.125turn);
+	line-height: tan(50grad);
+	transform: rotate(asin(-1));
+	transform: rotate(asin(sin(30deg + 1.0471967rad)));
+	transform: rotate(acos(-1));
+	transform: rotate(acos(cos(0 / 2 + 1 - 1)));
+	transform: rotate(atan(infinity));
+	transform: rotate(atan(e - 2.7182818284590452354));
+	transform: rotate(atan2(-infinity,-infinity));
+	transform: rotate(atan2(-infinity,infinity));
+	transform: rotate(atan2(-infinity,infinity));
+	transform: rotate(atan2(90, 15));
+}
+
+/* becomes */
+
+.trigonometry {
+	line-height: 0.70711;
+	line-height: sin(pi / 4);
+	line-height: 0.70711;
+	line-height: cos(.125turn);
+	line-height: 1;
+	line-height: tan(50grad);
+	transform: rotate(-90deg);
+	transform: rotate(asin(-1));
+	transform: rotate(90deg);
+	transform: rotate(asin(1));
+	transform: rotate(asin(sin(30deg + 1.0471967rad)));
+	transform: rotate(180deg);
+	transform: rotate(acos(-1));
+	transform: rotate(0deg);
+	transform: rotate(acos(1));
+	transform: rotate(acos(cos(0 / 2 + 1 - 1)));
+	transform: rotate(90deg);
+	transform: rotate(atan(infinity));
+	transform: rotate(0deg);
+	transform: rotate(atan(e - 2.7182818284590452354));
+	transform: rotate(-135deg);
+	transform: rotate(atan2(-infinity,-infinity));
+	transform: rotate(-45deg);
+	transform: rotate(atan2(-infinity,infinity));
+	transform: rotate(-45deg);
+	transform: rotate(atan2(-infinity,infinity));
+	transform: rotate(80.54deg);
+	transform: rotate(atan2(90, 15));
+}
+```
+
+[cli-url]: https://github.com/csstools/postcss-plugins/actions/workflows/test.yml?query=workflow/test
+[css-url]: https://cssdb.org/#trigonometric-functions
+[discord]: https://discord.gg/bUadyRwkJS
+[npm-url]: https://www.npmjs.com/package/@csstools/postcss-trigonometric-functions
+
+[Gulp PostCSS]: https://github.com/postcss/gulp-postcss
+[Grunt PostCSS]: https://github.com/nDmitry/grunt-postcss
+[PostCSS]: https://github.com/postcss/postcss
+[PostCSS Loader]: https://github.com/postcss/postcss-loader
+[PostCSS Trigonometric Functions]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-trigonometric-functions
+[CSS Values 4]: https://www.w3.org/TR/css-values-4/#trig-funcs