我猜在涉及PHP的网站品牌文件，但不是很确定。
是的，的确如此。您可以创建child theme 基于2017主题，添加并创建一个新的自定义标题。php文件及其所需的修改to style your header. 您自定义的2017头文件如下所示，
<?php
/**
* The header for our theme
*
* This is the template that displays all of the <head> section and everything up until <div id="content">
*
* @link https://developer.wordpress.org/themes/basics/template-files/#template-partials
*
* @package WordPress
* @subpackage Twenty_Seventeen
* @since 1.0
* @version 1.0
*/
?><!DOCTYPE html>
<html <?php language_attributes(); ?> class="no-js no-svg">
<head>
<meta charset="<?php bloginfo( \'charset\' ); ?>">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="profile" href="http://gmpg.org/xfn/11">
<?php wp_head(); ?>
</head>
<body <?php body_class(); ?>>
<div id="page" class="site">
<a class="skip-link screen-reader-text" href="#content"><?php _e( \'Skip to content\', \'twentyseventeen\' ); ?></a>
<header id="masthead" class="site-header" role="banner">
<?php get_template_part( \'template-parts/header/header\', \'image\' ); ?>
<?php if ( has_nav_menu( \'top\' ) ) : ?>
<div class="navigation-top">
<div class="wrap">
<?php get_template_part( \'template-parts/navigation/navigation\', \'top\' ); ?>
</div><!-- .wrap -->
</div><!-- .navigation-top -->
<?php endif; ?>
<button>
<!-- your custom button -->
</button>
</header><!-- #masthead -->
<?php
/*
* If a regular post or page, and not the front page, show the featured image.
* Using get_queried_object_id() here since the $post global may not be set before a call to the_post().
*/
if ( ( is_single() || ( is_page() && ! twentyseventeen_is_frontpage() ) ) && has_post_thumbnail( get_queried_object_id() ) ) :
echo \'<div class="single-featured-image-header">\';
echo get_the_post_thumbnail( get_queried_object_id(), \'twentyseventeen-featured-image\' );
echo \'</div><!-- .single-featured-image-header -->\';
endif;
?>
<div class="site-content-contain">
<div id="content" class="site-content">
注意我插入自定义项的位置
button 带有html注释
<!-- your custom button -->