index.php

<?php
/**
 * The main template file.
 *
 * This is the most generic template file in a WordPress theme
 * and one of the two required files for a theme (the other being style.css).
 * It is used to display a page when nothing more specific matches a query.
 * E.g., it puts together the home page when no home.php file exists.
 * Learn more: http://codex.wordpress.org/Template_Hierarchy
 *
 * @package storefront
 */
get_header();

$class = '';
//is blog 
if (is_home()) {
    get_header('blog'); //header-blog.php
    $class = 'blog-page';
    ?>
    <div class="container">
        <div class="row">
            <div class="col-md-12">
                <?php
            }
            ?>

            <div id="primary" class="content-area <?php echo $class; ?>">
                <main id="main" class="site-main" role="main">

                    <?php
                    if (have_posts()) :

                        get_template_part('loop');

                    else :

                        get_template_part('content', 'none');

                    endif;
                    ?>

                </main><!-- #main -->
            </div><!-- #primary -->



            <?php
            do_action('storefront_sidebar');

            if (is_home()) {
                ?>
            </div>
        </div>
    </div>
    <?php
}
get_footer();