Custom Header | HTML Version

function custom_divi_header() {

//Insert HTML here

}
add_action( 'et_html_main_header', 'custom_divi_header' );

Custom Header | Logo Code for HTML Version

<?php
				$logo = ( $user_logo = et_get_option( 'divi_logo' ) ) && '' != $user_logo
					? $user_logo
					: $template_directory_uri . '/images/logo.png';

				ob_start();
			?>
            <div class="logo_container">
					<span class="logo_helper"></span>
					<a href="<?php echo esc_url( home_url( '/' ) ); ?>">
						<img src="<?php echo esc_attr( $logo ); ?>" alt="<?php echo esc_attr( get_bloginfo( 'name' ) ); ?>" id="logo" data-height-percentage="<?php echo esc_attr( et_get_option( 'logo_height', '54' ) ); ?>" />
					</a>
			</div>
			    <?php
				$logo_container = ob_get_clean();

				/**
				 * Filters the HTML output for the logo container.
				 *
				 * @since ??
				 *
				 * @param string $logo_container
				 */
				echo apply_filters( 'et_html_logo_container', $logo_container );
        ?>

Custom Header | Menu code for HTML Version

<?php
							$menuClass = 'nav';
							if ( 'on' == et_get_option( 'divi_disable_toptier' ) ) $menuClass .= ' et_disable_top_tier';
							$primaryNav = '';

							$primaryNav = wp_nav_menu( array( 'theme_location' => 'primary-menu', 'container' => '', 'fallback_cb' => '', 'menu_class' => $menuClass, 'menu_id' => 'top-menu', 'echo' => false ) );

							if ( '' == $primaryNav ) :
						?>
							<ul id="top-menu" class="<?php echo esc_attr( $menuClass ); ?>">
								<?php if ( 'on' == et_get_option( 'divi_home_link' ) ) { ?>
									<li <?php if ( is_home() ) echo( 'class="current_page_item"' ); ?>><a href="<?php echo esc_url( home_url( '/' ) ); ?>"><?php esc_html_e( 'Home', 'Divi' ); ?></a></li>
								<?php }; ?>

								<?php show_page_menu( $menuClass, false, false ); ?>
								<?php show_categories_menu( $menuClass, false ); ?>
							</ul>
						<?php
							else :
								echo( $primaryNav );
							endif;
						?>
						</nav>

With library item

function custom_divi_header() {

echo do_shortcode('[et_pb_section global_module="xxx"][/et_pb_section]'); // Change XXX to library items id (you can find the library item id when editing the library item if you look in the url bar you will see number after .mysite.com/wp-admin/post.php?post=xxx )

}
add_action( 'et_html_main_header', 'custom_divi_header' );