docs: add quickstart sections postcss and tailwind config

Author: MGREMY

apps/docs/docs/customize/theming/index.md

@@ -5,6 +5,8 @@ keyword: ThemingPage
 You can use the theme directive from tailwind to define any style related classes, such as the color
 palette, fonts, breakpoints, and more.
 
+Here is the `primary` color theme used for this documentation :
+
 ```css
 @theme {
   /* Primary */

apps/docs/docs/getting-started/quickstart/index.md

@@ -12,7 +12,7 @@ Angular library.
 Make sure that TailwindCSS is installed.
 
 ```bash
-npm install tailwindcss
+npm install tailwindcss @tailwindcss/postcss postcss
 ```
 
 Install Flowbite as a dependency using NPM by running this command:
@@ -25,8 +25,27 @@ npm install flowbite-angular ng-primitives @ng-icons/core
 
 Make sure to use the flowbite-angular configuration preset in your styles.css
 
+> **Note** If your `node_modules` folder is located above the parent directory (e.g., in a monorepo
+> setup), you may need to adjust the path with additional `../` to correctly reference it, such as
+> `@source "../../../node_modules/flowbite-angular";`.
+
 ```css
 @import 'tailwindcss';
 
-@source "node_modules/flowbite-angular";
+@source "../node_modules/flowbite-angular";
+```
+
+> **Note** If you want a working `primary` color definition, see `*ThemingPage` page
+
+## PostCSS configuration
+
+Create a `postcss.config.json` file in the root of your project and add the `@tailwindcss/postcss`
+plugin to your PostCSS configuration.
+
+```json
+{
+  "plugins": {
+    "@tailwindcss/postcss": {}
+  }
+}
 ```