Bootstrap 5 buttons are not displayed correctly

[mariantanase]

I've notice that the css styles of the bootstrap 5 button classes do not seem to be loaded. In a custom html module, I have inserted the following code: <button type="button" class="btn btn-warning btn-lg px-4 me-md-2">Scopri Gantry!</button></div>

I expect it to display as seen on this page: Bootstrap 5 Butons

But no style was applied. The classes warning, danger,... do not seem to be interpreted. On my test site, the .btn class, currently adds a transparent background, but the background button should have a specific color Do I miss something ?

Gantry 5.5.8 Joomla 4.1.0 RC4 PHP 7.4.28