Child theme and overrides

Put every change to the theme's code in the child theme (or a plugin), so theme updates don't overwrite it. BlueTheme ships a ready-made child theme, bluetheme-child.

The child theme

bluetheme-child/
  style.css       theme header; your CSS goes here
  functions.php   loads style.css after the theme's styles, and the child's translations
  languages/      your .po/.mo files for the bluetheme-child text domain
  screenshot.png

Install both zips in Appearance → Themes → Add New, then activate BlueTheme Child. Theme Options, templates, menus and widgets stay as they are: they belong to the site, not to the active theme.

CSS: the child's style.css loads after the theme's stylesheets. Use the theme's custom properties (var(--bt-color-primary), var(--bt-radius)) and logical properties (margin-inline-start) so your CSS follows Theme Options and works in both directions.
PHP: add actions and filters in functions.php, prefixed with your own name. Every hook the theme offers is in the hooks reference.
Translations: strings in the child use the bluetheme-child text domain, loaded from languages/.

Overriding template files

Copy a file from bluetheme/ to the same path in bluetheme-child/ and edit the copy. WordPress loads the child's version.

File	What it prints
`header.php`, `footer.php`	The document head and the start and end of the page. The header and footer themselves come from templates or `template-parts/header` and `template-parts/footer`.
`index.php`, `archive.php`, `search.php`, `single.php`, `page.php`, `404.php`	The page types.
`template-parts/content/*.php`	A post in a list, a single post, a page, a search result, "nothing found".
`template-parts/blog/*.php`	Blog parts: the post loop, filters, the author box, related posts, previous and next.
`template-parts/header/*.php`	The classic header (when no header template applies), the mobile header, the menu panel, the search panel, the action bar.
`template-parts/footer/site-footer.php`	The classic footer (when no footer template applies).
`template-parts/portfolio/*.php`	The portfolio archive and project page.
`template-parts/page-title.php`, `pagination.php`	The title bar and page numbers.
`comments.php`, `searchform.php`, `sidebar.php`	As in any theme.

Copy as few files as you can. A copied file doesn't get the theme's later fixes, so prefer a hook when one exists:

bluetheme_before_header, bluetheme_after_header, bluetheme_before_content, bluetheme_after_content, bluetheme_before_footer, bluetheme_after_footer: print something at that point on every page. Theme Options → Global → Hooks does the same without code.
bluetheme_layout, bluetheme_has_sidebar, bluetheme_subheader_title, bluetheme_copyright: change a value the templates use.

Pages made with the builder and headers, footers and other templates made in Templates are not files; change them in the builder.

WooCommerce templates

BlueTheme styles WooCommerce through hooks and CSS and doesn't replace its template files. Override one the WooCommerce way: copy it from wp-content/plugins/woocommerce/templates/ to bluetheme-child/woocommerce/ at the same path. Single product and shop pages can also be built as templates in the builder, with the product elements.

Adding to the builder

Elements: a folder in bluetheme-child/elements/. See adding an element. Every element can be used on pages and in every kind of template; the header category only groups the ones made for headers and footers.
Pre-built sections: design the section in the builder, save it as a template and export it (Templates → Export). Then add the exported section with the bluetheme_library_sections filter:

add_filter( 'bluetheme_library_sections', function ( array $sections ): array {
	$file = json_decode( file_get_contents( get_stylesheet_directory() . '/sections/promo.json' ), true );
	// Id => [ label, category, section node ]. Categories: hero, about, services,
	// features, team, pricing, testimonials, cta, contact, stats.
	$sections['child_promo'] = array( __( 'Promo', 'bluetheme-child' ), 'cta', $file['document']['sections'][0] );
	return $sections;
} );

Header and footer presets in the "Add template" gallery: the bluetheme_template_presets filter, with id => [ label, category, description, sections, settings ] for type header or footer.
Template types: the bluetheme_template_types filter.
More post types in the builder: the bluetheme_builder_post_types filter.

Adding options

Add your own Theme Options sections and fields with the bluetheme_options_sections filter, and read them with Options::get(). See Theme Options internals.

Icons and fonts

Icon packs: upload a zip of SVG files with Upload icon pack… in any icon picker, or register a pack with the bluetheme_icon_packs filter.
Fonts: upload WOFF2 files in Theme Options → Fonts → Custom fonts, or add families with the bluetheme_fonts_families filter.