Why include_once including only HTML file not css?

Question

include_once"../registration/registration/registration_page.php";
Its include only HTML part.CSS part was not applied on page.php. While opening it separately it working fine.

Answer 1

to css file u need to use
link tag in html
include ,include_once ,require and require_once is used with php files
to ur css file:
<link rel="stylesheet" href="part.css">