When you install WordPress and head to Appearance > Themes, you face a choice that shapes everything about how you build and edit your site. Block themes and classic themes look similar in the theme browser, but they use completely different editing systems under the hood. Block themes use the Site Editor and let you customize headers, footers, and every template part without touching PHP files. Classic themes rely on PHP-based templates and the Customizer for global settings. This article walks you through the practical differences, what each system actually does when you click buttons, and which one matches the way you want to work.
The setup
Appearance > Themes in your WordPress dashboard. Block themes show “Customize” and “Editor” buttons, while classic themes show only “Customize.” The Editor button opens the Site Editor, a full-screen interface for editing templates. The Customize button opens the older Customizer panel. This choice determines which files your theme uses and where your design settings live.
How block themes store templates and settings
Block themes keep their layout templates as HTML files inside a templates folder in your theme directory. When you open the Site Editor from Appearance > Editor, you see a list of templates like Single Posts, Pages, Archive, and Index. Click any template and you edit it directly in the block editor, the same interface you use for posts and pages.
Every piece of the template is a block. Your header is a Header block, your footer is a Footer block, your post content is a Post Content block. You drag blocks around, adjust spacing with visual controls, and change colors by clicking elements. When you save, WordPress writes those changes back to HTML files or stores them in the database as user customizations, depending on whether you edited the theme template or created a custom version.
Global settings like colors, typography, and spacing live in a theme.json file at the root of your theme folder. You can edit this file directly if you know JSON syntax, but most block themes also let you adjust these settings through the Site Editor’s Styles panel. Click the black-and-white icon in the top toolbar and you see color palettes, font families, and layout settings. Changes here update the theme.json configuration, which applies across every template automatically.
You never write PHP to change a header or add a sidebar. Everything happens in the visual editor. That means you can build a completely custom site design without opening a code editor, but it also means you work within the constraints of what blocks can do. If you need a layout pattern that no block supports, you either wait for a plugin to add that block or build it yourself.
How classic themes organize files and customization
Classic themes store templates as PHP files. Your homepage layout lives in index.php or front-page.php, your single post layout lives in single.php, and your header code sits in header.php. When WordPress renders a page, it loads the appropriate PHP template, runs the code, and outputs HTML.
To customize a classic theme, you use Appearance > Customize. This opens a sidebar panel with sections for Site Identity, Colors, Header Image, Menus, Widgets, and Homepage Settings. Each option in the Customizer is a setting the theme developer registered using PHP functions. You pick a color, upload a logo, or arrange menu items, and WordPress saves those choices to the database. The theme’s PHP templates read those saved settings and output the corresponding HTML.
If the Customizer does not expose a setting you need, you edit the PHP files directly or add CSS in the Additional CSS panel. Want to change your footer layout? You open footer.php in a code editor, modify the HTML structure, and upload the changed file. This gives you complete control, but it requires you to understand at least basic PHP and HTML. Most users who go this route create a child theme so updates to the parent theme do not overwrite their changes.
Classic themes have been the standard since WordPress launched, so they integrate with a huge library of plugins, page builders, and customization tutorials. When you search for how to do something in WordPress, most guides assume you are using a classic theme. That documentation advantage matters when you hit a problem at midnight and need a fix.
What breaks
You install a plugin that requires the Customizer, but your block theme does not have one
Some older plugins register their settings in the Customizer. When you install them on a block theme, they tell you to go to Appearance > Customize, but that menu item does not exist because block themes skip the Customizer entirely. The plugin still loads, but you cannot access its settings panel.
The fix is to check if the plugin offers Site Editor integration or a standalone settings page under Settings or Tools. If it does not, contact the developer or switch to a plugin that supports block themes. You can also temporarily switch to a classic theme, configure the plugin, then switch back, though settings may not persist correctly.
You edit a template in the Site Editor and your changes disappear after a theme update
When you customize a template in the Site Editor, WordPress saves your version separately as a user customization. Theme updates replace the original template files but should leave your custom versions intact. However, if the theme changes its template structure significantly, your custom template may reference blocks or layout patterns that no longer exist, causing the Site Editor to revert to the updated default.
To prevent this, export your custom templates before updating. Go to Appearance > Editor > Templates, click the three-dot menu on each customized template, and choose Export. After the update, compare your exported HTML to the new default and manually merge any needed changes. Alternatively, use a child theme and store your custom templates there.
Your classic theme layout looks broken after switching to the block editor for posts
Classic themes were designed when the classic editor was standard. They apply CSS that expects the post content to be wrapped in certain classes and tags that the classic editor outputs. When you enable the block editor, it outputs different HTML structures for paragraphs, images, and embeds. Your theme CSS does not target these new classes, so spacing, alignment, and typography look wrong.
The fix is to add CSS that targets block editor classes. Most classic themes released after 2018 include block editor support, but older themes need manual updates. You can add rules in Appearance > Customize > Additional CSS, or edit style.css in a child theme. Look for classes like .wp-block-image, .wp-block-paragraph, and .alignwide and apply the same spacing and font styles you use for classic editor content.
FAQs
Can I use page builders like Elementor with block themes?
Yes, but you lose some benefits. Elementor works by replacing the block editor with its own visual builder, so you edit page content in Elementor but still manage your header, footer, and archive templates in the Site Editor. Some page builders like Elementor also offer their own theme builder that can replace the Site Editor entirely, letting you design headers and footers in the page builder interface. Just know you are mixing two systems, which can create conflicts with CSS loading order and template hierarchy.
Do block themes load faster than classic themes?
Not automatically. Block themes can be lighter because theme.json consolidates settings that classic themes scatter across multiple PHP files and hooks, and the Site Editor generates cleaner HTML. But a poorly coded block theme with bloated JavaScript for fancy block animations can easily be slower than a well-optimized classic theme. Performance depends on how the theme developer writes the code, not which system they use.
Can I convert a classic theme to a block theme?
Technically yes, but it is easier to build a new block theme from scratch. You need to convert every PHP template to HTML block markup, move all Customizer settings into theme.json, and replace widget areas with block-based template parts. WordPress provides a migration tool for some themes, but complex classic themes with custom post type templates, WooCommerce integration, and extensive Customizer options require manual translation. Most developers treat it as a full rebuild rather than a conversion.
Will classic themes eventually stop working?
No. WordPress maintains backward compatibility aggressively, and millions of sites run classic themes. The Customizer and PHP template system still receive updates and security patches. However, new WordPress features focus on the Site Editor and block themes, so classic themes will not get native support for features like style variations, template editing in the admin, or global settings panels. You can keep using a classic theme indefinitely, but you miss out on the newest editing tools.
Which system works better for WooCommerce stores?
Classic themes still dominate WooCommerce because most shop owners need granular control over product page layouts, cart flows, and checkout forms. WooCommerce templates are PHP files, and customizing them in a classic theme means editing those files or using hooks. Block themes can run WooCommerce, and WooCommerce now offers product-related blocks, but you have fewer options for custom product layouts without writing custom blocks. If you plan heavy shop customization, start with a classic WooCommerce theme.
Verdict: Start with a block theme if you want to customize your entire site visually without editing code and you do not rely on plugins that require the Customizer. Start with a classic theme if you need deep WooCommerce integration, plan to use a third-party page builder, or prefer the control and documentation ecosystem that comes with PHP templates.
