silverstripe-cms/templates/SilverStripe/CMS/Controllers/Includes/CMSPagesController_Content.ss

<div id="pages-controller-cms-content" class="flexbox-area-grow fill-height cms-content $BaseCSSClasses" data-layout-type="border" data-pjax-fragment="Content">
    <div class="cms-content-header north vertical-align-items">
        <div class="cms-content-header-info fill-width vertical-align-items">
            <% if $TreeIsFiltered %>
                <a class="btn btn-secondary font-icon-left-open-big toolbar__back-button btn--no-text" href="$BreadcrumbsBacklink">
                    <span class="sr-only"><%t SilverStripe\Admin\LeftAndMain.NavigateUp "Return to Pages" %></span>
                </a>
            <% end_if %>
            <% include SilverStripe\\Admin\\CMSBreadcrumbs %>
            <% include SilverStripe\\CMS\\Controllers\\CMSMain_Filter %>
        </div>
    </div>

    <div class="flexbox-area-grow fill-height cms-content-fields ui-widget-content cms-panel-padded">
        $Tools
        $PageList
    </div>
</div>