Backdrop CMS: Full width layout to allow blocks in the content region to be full width.

block.tpl.php

<?php
/**
 * @file
 * Template for outputting the default block styling within a Layout.
 *
 * Variables available:
 * - $classes: Array of classes that should be displayed on the block's wrapper.
 * - $title: The title of the block.
 * - $title_prefix/$title_suffix: A prefix and suffix for the title tag. This
 *   is important to print out as administrative links to edit this block are
 *   printed in these variables.
 * - $content: The actual content of the block.
 */
?>
<div class="<?php print implode(' ', $classes); ?>"<?php print backdrop_attributes($attributes); ?>>
  <!-- Block wrapper with container classes. -->
  <div class="block-wrapper container container-fluid">
  <?php print render($title_prefix); ?>
  <?php if ($title): ?>
    <h2 class="block-title"><?php print $title; ?></h2>
  <?php endif; ?>
  <?php print render($title_suffix); ?>

    <div class="block-content">
      <?php print render($content); ?>
    </div>
  </div><!-- /.block-wrapper -->
</div>

layout--boxton-full-width.tpl.php

<?php
/**
 * @file
 * Template for the custom Boxton Full Width layout.
 *
 * The custom Boxton Full Width layout allows blocks in the content region to be full width, e.g. to define alternating background colors for different Views blocks.
 *
 * Variables:
 * - $title: The page title, for use in the actual HTML content.
 * - $messages: Status and error messages. Should be displayed prominently.
 * - $tabs: Tabs linking to any sub-pages beneath the current page
 *   (e.g., the view and edit tabs when displaying a node.)
 * - $action_links: Array of actions local to the page, such as 'Add menu' on
 *   the menu administration interface.
 * - $classes: Array of CSS classes to be added to the layout wrapper.
 * - $attributes: Array of additional HTML attributes to be added to the layout
 *     wrapper. Flatten using backdrop_attributes().
 * - $content: An array of content, each item in the array is keyed to one
 *   region of the layout. This layout supports the following sections:
 *   - $content['header']
 *   - $content['top']
 *   - $content['content']
 *   - $content['bottom']
 *   - $content['footer']
 */
?>
<div class="layout--boxton layout--boxton-fullwidth <?php print implode(' ', $classes); ?>"<?php print backdrop_attributes($attributes); ?>>
  <div id="skip-link">
    <a href="#main-content" class="element-invisible element-focusable"><?php print t('Skip to main content'); ?></a>
  </div>

  <?php if ($content['header']): ?>
    <header class="l-header" role="banner" aria-label="<?php print t('Site header'); ?>">
      <div class="l-header-inner container container-fluid">
        <?php print $content['header']; ?>
      </div>
    </header>
  <?php endif; ?>

  <div class="l-wrapper">
    <!-- Remove container classes from wrapper inner. -->
    <div class="l-wrapper-inner">

      <?php if ($messages): ?>
        <!-- Add container classes. -->
        <div class="l-messages container container-fluid" role="status" aria-label="<?php print t('Status messages'); ?>">
          <?php print $messages; ?>
        </div>
      <?php endif; ?>

      <!-- Add container classes. -->
      <div class="l-page-title container container-fluid">
        <a id="main-content"></a>
        <?php print render($title_prefix); ?>
        <?php if ($title): ?>
          <h1 class="page-title"><?php print $title; ?></h1>
        <?php endif; ?>
        <?php print render($title_suffix); ?>
      </div>

      <?php if ($tabs): ?>
        <!-- Add container classes. -->
        <nav class="tabs container container-fluid" role="tablist" aria-label="<?php print t('Admin content navigation tabs.'); ?>">
          <?php print $tabs; ?>
        </nav>
      <?php endif; ?>

      <?php print $action_links; ?>

      <?php if (!empty($content['top'])): ?>
        <!-- No container classes for top region, they are part of the hero block. -->
        <div class="l-top">
          <?php print $content['top']; ?>
        </div>
      <?php endif; ?>

      <!-- No container classes for content region, they will be added to blocks content. -->
      <div class="l-content" role="main" aria-label="<?php print t('Main content'); ?>">
        <?php print $content['content']; ?>
      </div>

      <?php if (!empty($content['bottom'])): ?>
        <!-- Add container classes. -->
        <div class="l-bottom container container-fluid">
          <?php print $content['bottom']; ?>
        </div>
      <?php endif; ?>

    </div><!-- /.l-wrapper-inner -->
  </div><!-- /.l-wrapper -->

  <?php if ($content['footer']): ?>
    <footer class="l-footer"  role="footer">
      <div class="l-footer-inner container container-fluid">
        <?php print $content['footer']; ?>
      </div><!-- /.container -->
    </footer>
  <?php endif; ?>
</div><!-- /.layout--boxton(-full-width) -->