[Theme – Rider] Fixed header's bloc

Hi,

i got a problem with the head’s bloc. I put an image. And i would like to know where is the function, in wich file, could i find how to fixe this header on the top, and not downing with the scrollbar.

I founded that the function in the header.php file is “<?php wp_head(); ?>”, and it’s calling general_template.php, but after that, inside this file, i cannot find what i’m searching.

So, can you lighting me ?
Thank you, very much.
See you soon.