Update Tailwind v4+ guidelines (#321)

* docs: update Tailwind v4+ guidelines with configuration guidelines

Signed-off-by: Pushpak Chhajed <pushpak1300@gmail.com>

* Revert 4.1 change

Signed-off-by: Pushpak Chhajed <pushpak1300@gmail.com>

* Update core.blade.php

---------

Signed-off-by: Pushpak Chhajed <pushpak1300@gmail.com>
Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: pushpak1300

.ai/tailwindcss/4/core.blade.php

@@ -2,6 +2,13 @@
 
 - Always use Tailwind CSS v4 - do not use the deprecated utilities.
 - `corePlugins` is not supported in Tailwind v4.
+- In Tailwind v4, configuration is CSS-first using the `@theme` directive — no separate `tailwind.config.js` file is needed.
+@verbatim<code-snippet name="Extending Theme in CSS" lang="css">
+@theme {
+  --color-brand: oklch(0.72 0.11 178);
+}
+</code-snippet>
+@endverbatim
 - In Tailwind v4, you import Tailwind using a regular CSS `@import` statement, not using the `@tailwind` directives used in v3:
 @verbatim
 <code-snippet name="Tailwind v4 Import Tailwind Diff" lang="diff">