Is it possible to add a page that I have created the entire content in PHP add the Joomla template to it? That is, I have a website created by Joomla, and a menu item points to a PHP file that I have created myself, but I don't want to integrate it through any extension, just to know if it is possible to add the CSS of said template to This part I enter.
Well, that is the purpose of the CSS to give consistency to the design
just add in the
<head>
of your PHPwhere style.css is your css file