Relative paths in css files are relative to the css file location, but in PHP they are relative to the website URL not to the php file location in the server.
So to make sure you get the right URL for any resource you want to load in PHP files you can use the function get_template_directory_uri()
like this:
"<?php echo get_template_directory_uri(); ?>":
For example in img the attribute src would be:
<img src="https://wordpress.stackexchange.com/questions/300896/<?php echo get_template_directory_uri(); ?>/media/img/contact-1.jpg" />
And so on for js files and css files.
Notice:
In the case of using a Child theme, use this function instead get_stylesheet_directory_uri() the same way:
<img src="https://wordpress.stackexchange.com/questions/300896/<?php echo get_stylesheet_directory_uri(); ?>/assets/img.jpg" />
Otherwise the get_template_directory_uri() function in this case will only return the current parent theme URL and not the URL of the child theme which you are using in this case.