Remove Header and style.css from Specific Post template

I want to add some custom code so I’ve created a custom post file with the following content.

<?php
/*
 * Template Name: Custom App
 * Template Post Type: post, page, product
 */

 ?>
 <?php get_header(); ?>
 App Code here...

I want to remove the header element <header id="header" class="main-header"> and style.css from the custom post using function.php file.

I want to keep <?php get_header(); ?> because of yoast SEO and some analytics scripts.

I don’t want to hide the main-header using CSS display:none property