PHP is a server side scripting language. It is incredibly powerful, and understanding even a little bit can make your life much easier.
Create a new folder called “php-trick” and copy all of the files from the assets folder into it. Then, create two files in the root folder called header.php and footer.php.
Copy the “reusable code” into the coordinating file, then edit each page to call the reusable code using the code:
<?php include('header.php'); ?>
<?php include('footer.php'); ?>