Is it possible to Change the style on one specific page

in the template im trying i can’t get it to do what i want.

the site is : https://kubestudio.com/web/wordpress

when you click the 2nd button portfolio a sub menu opens, and what i want is that on those sub menus the “MainWrapper” is 0px wide instead of the 500 or whatever of the other pages.

Now those sub-menus ( the sports one for example ) Answer to a file called : single-portfolio.php

with this code:

<?php 

get_header(2); 

$gallery_id = (get_post_meta($post->ID, THEME_METABOX . 'gallery_id', true) == "") ? null : get_post_meta($post->ID, THEME_METABOX . 'gallery_id', true);
$gallery_columns = (get_post_meta($post->ID, THEME_METABOX . 'gallery_columns', true) == "") ? 3 : get_post_meta($post->ID, THEME_METABOX . 'gallery_columns', true);

$heading_text = (get_post_meta($post->ID, THEME_METABOX . "heading_text", true) == "") ? get_the_title() : get_post_meta($post->ID, THEME_METABOX . "heading_text", true);
?>

<!-- start mainWrapper -->
<div id="mainWrapper">
	<h1 id="pageHeading"><?php echo $heading_text;?></h1>
	<!-- start content -->
	<div id="content">
		<!--start single post-->
		<div id="singlePost">
			<!-- start post -->
			<div <?php post_class("last"); ?>>
			<?php 

			if (have_posts()) : while (have_posts()) : the_post();

			$image_url_big = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'full');

			?>

			<div class="postContent">

				<?php //get_template_part('templates/entrymeta'); ?>

				<?php 

				the_content(); 

				?>   

			</div>

			<?php 

			endwhile; endif;
			?>

			<?php
			if ( !post_password_required() ) :

				comments_template();
			endif;
			?>
			</div>
			<!-- end post -->
		</div>
		<!-- end single post-->
	</div>
	<!-- end content -->
</div>
<!-- end mainWrapper -->

<?php get_template_part('templates/sidewrapper'); ?>

<?php get_footer(); ?>

I tryed changing that PHP to not load the MainWrapper but can’t get it to work, so im thinking on an alternative way changing the style of this specific page.

Now i guess this page gets the Style from the Get_header , so i thought about creating a new header that calls a new style.css ( style2.css for example ) and in this style2.css i will change the width of the Mainwrapper wich works because i tried on the style.css

Now how do i do this?

i mean getting the single-portfolio.php to load style2.css instead of style.css ?

thanks a lot!

i have another post open to try to correct the issue with php but not finding a solution so maybe CSS works easier.

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