Can’t find a class element in my style sheets

I’m developing an in-house Intranet site that’s hosted on a private server so I can’t link to it here. Please be gentle with me … I’m teaching myself CSS and php code as I go.

I would like to change the layout of my page.php file so that the breadcrumbs and header are child elements of the #primary section on each page, instead of child elements of the container. When I use the Inspect window in Chrome, I can see the .breadcrumb-wrapper element, and I can move it and the header element to the correct placement; but I don’t know how or where to make this change permanent in the style sheets or the php files. None of the CSS files in my theme or plugins include that .breadcrumb-wrapper element!

I can see where some of the html elements are defined on the page.php file, but I don’t know how to write or change the code to call the appropriate breadcrumb links or page title.

This is the source code for a sample page:

 <div class="container">
        <div class="breadcrumb-wrapper" itemscope itemtype="https://schema.org/BreadcrumbList">
                <div id="crumbs" itemprop="itemListElement" itemscope itemtype="https://schema.org/ListItem">
                    <a href="https://10.1.1.199" itemprop="item">Home</a> 
                    <span class="separator">></span>
                    <span class="current">Electrical</span>
                </div><!-- #crumbs -->
        </div><!-- .breadcrumb-wrapper -->
        <header class="page-header"><h1 class="page-title">Electrical</h1>
        </header><!-- .page-header -->
        <div class="content-grid">
	        <div id="primary" class="content-area">
		        <main id="main" class="site-main">
                                <article id="post-193" class="post-193 page type-page status-publish hentry">
                                        <div class="entry-content" itemprop="text"><p>Info related to Electrical</p>
                        	        </div><!-- .entry-content -->
                                </article>
                        </main>
                 </div><!-- #primary -->
        </div><!-- .content-grid -->
</div><!-- .container -->