A WordPress theme controls how your site looks and behaves — layout, colours, fonts, the whole visual experience. What most first-time owners do not realise is that there are two fundamentally different kinds of theme, with different editors, different capabilities, and different philosophies. Classic themes are the way WordPress worked for fifteen years. Block themes are the way WordPress works now. Choosing between them affects how you customise your site every day, how deeply you can modify it without touching code, and how future-proof your investment is. This guide explains both, compares them side by side, and helps you decide which is right.
Why theme type matters · Classic themes: the traditional approach · Block themes: the modern standard · Block vs classic side by side · How to tell which type you have · Which should you choose? · Hybrid themes: the middle ground · Anatomy of a WordPress theme · Performance and SEO considerations · Frequently asked questions
The theme you pick shapes three things:
For most new UK business sites in 2026, a block theme is the better starting point. Classic themes still have a role for specific situations. Understanding both helps you make an informed choice rather than just picking whatever the hosting control panel installs first.
Classic themes have been part of WordPress since version 1.0 in 2003. They use PHP template files to define page structure, and the Customiser for visual adjustments.
Access the Customiser from Appearance > Customize. A live-preview sidebar lets you adjust:
Changes show in the live preview before publishing. Scope is limited to what the theme developer exposes — editing the header or footer structure usually requires PHP edits or a page builder plugin.
Astra, GeneratePress, OceanWP and Hello Elementor remain popular. They are lightweight, highly configurable through their own settings panels, and work well with page builders like Elementor, Divi and Beaver Builder.
Older WordPress defaults (Twenty Twenty-One, Twenty Twenty, Twenty Nineteen) are classic themes.
Block themes arrived with WordPress 5.9 (January 2022) and the Twenty Twenty-Two default. They replace the Customiser, widgets and menus with a single unified editing experience: the Full Site Editor.
Access from Appearance > Editor. You edit every part of the site visually using the same block-based approach as the content editor.
Visual, block-based, consistent. The same editor you use for pages controls your header, footer and templates. No CSS, no PHP, no third-party page builder required.
Twenty Twenty-Five (current WordPress default) — clean, flexible, block-first by design.
Other strong options: Kadence (block version), Blocksy Companion, Spectra One, Ollie, Frost, Pendant. Recent WordPress defaults (Twenty Twenty-Four, Twenty Twenty-Three, Twenty Twenty-Two) are all block themes.
Block themes often ship with pre-built style variations — colour + typography combinations you apply with one click. Twenty Twenty-Five includes nine style variations, each giving the same layout a distinctive look.
| Feature | Block theme | Classic theme |
|---|---|---|
| Customisation tool | Full Site Editor | Customiser |
| Header / footer editing | Full visual control with blocks | Limited; PHP editing often needed |
| Navigation | Navigation block in editor | Appearance > Menus or Customiser |
| Widgets | Not used — blocks replace them | Sidebars and widget areas |
| Template control | Create and edit templates visually | PHP template files |
| Global styles | One panel for colours, fonts, spacing | Theme-specific settings plus CSS |
| Style variations | Built-in | Rare |
| Learning curve | Moderate, consistent | Lower initially, capped by theme options |
| Future focus | Core development direction | Still supported, no longer primary |
| Page builder dependency | Rarely needed | Often used to overcome limits |
Quickest check from the WordPress dashboard:
Another method: the theme's page on WordPress.org usually says "Block theme" in the description when it is one. Some themes support both modes — more on those under Hybrid themes.
Most UK SMEs starting a new WordPress site in 2026 should default to a block theme. Twenty Twenty-Five is a reasonable zero-cost starting point. Kadence (block version), Astra (block version), Blocksy offer more depth if you need it. Retaining a classic theme is a deliberate choice rather than a default.
Some themes support both approaches simultaneously. They can be used like a classic theme (with the Customiser) while also offering block templates through the Full Site Editor for those who want them.
Examples: Astra (originally classic, now offers both modes), Blocksy, Neve. Useful when a team wants to transition gradually — start with the Customiser, move parts of the site to FSE as they learn.
Downside: the dual approach can be confusing. Some settings live in the Customiser; others in the Full Site Editor; some in both with conflicts. Pick one mode and commit to it.
Under the hood, a theme is a folder in wp-content/themes/. Key files:
Most users never touch these files. Block theme users edit via the FSE interface; classic theme users edit via the Customiser plus plugin extensions. Direct file editing is reserved for child themes or developer-led customisation.
Theme choice affects site speed and SEO in several ways.
Some themes (particularly premium classic themes with bundled page builders) weigh 2–5x what a lean theme weighs. GeneratePress, Blocksy and Twenty Twenty-Five are lightweight. Divi and Avada are heavy. Lighter themes rank better on Core Web Vitals.
Classic themes often require companion plugins (theme's page builder, theme's sidebar plugin). Each adds weight. Block themes are typically self-contained.
Modern themes output proper semantic HTML (<article>, <header>, <nav>) and include basic schema. Older themes sometimes use generic <div> soup that Google ranks worse. Check with View Source on a typical page.
Themes marked "accessibility-ready" on WordPress.org have passed basic WCAG checks. For UK public-sector sites, pick accessibility-ready themes as a starting point.
Can I switch from a classic theme to a block theme later?
Yes. Switch in Appearance > Themes. Content (pages, posts, media) remains unchanged. Widgets and menus may need reconfiguring since block themes handle them differently. Always clone to staging first via the Plesk WordPress Toolkit and test before switching on production.
Is the Twenty Twenty-Five theme good enough for a business site?
Yes, honestly. Twenty Twenty-Five is clean, lightweight, full-site-editable and ships with nine style variations. Many UK businesses launch and stay with it, just customising colours and fonts.
Can I use Elementor with a block theme?
Yes. Elementor works on block themes, though part of its value (heavy design override) overlaps with what FSE already does. If you use Elementor you are essentially paying for features a block theme plus FSE give you for free.
Do block themes work with WooCommerce?
Yes. WooCommerce is compatible with both theme types. WooCommerce provides block-based shop templates that integrate with FSE; product / cart / checkout blocks work in block themes natively.
What is the difference between a theme and a page builder?
A theme defines the overall site structure (header, footer, templates, global styles). A page builder (Elementor, Divi, Beaver Builder) overrides theme templates with its own visual editor for individual pages. Block themes with FSE now provide most page-builder functionality natively.
How do I change my theme?
Appearance > Themes > Add New Theme. Install and preview first. When ready, click Activate. Back up first — theme switches occasionally reveal layout issues.
Why does my theme say "Update available" every few weeks?
Theme developers push security and compatibility updates regularly. Apply updates promptly — outdated themes are a security risk.
Are free themes as good as paid themes?
Free themes from the WordPress.org directory are genuinely production-ready. Paid themes offer more templates, pre-built pages, and paid support. For most UK small businesses, a free theme like GeneratePress or Twenty Twenty-Five is sufficient. Paid upgrades are optional.
Can I use multiple themes on one site?
No. One active theme at a time. The exception is WordPress multisite, where each subsite can have its own theme.
How often should I change themes?
Rarely. A good theme should last 3–5 years with incremental updates and customisation. Frequent theme changes disrupt visitors, break SEO and waste time. Settle on a theme, customise it thoroughly, and keep it.
Launch your WordPress site on smartxhosting.uk
UK hosting with the Plesk WordPress Toolkit, LiteSpeed Cache, Redis object caching, free Let’s Encrypt SSL, free CDN and daily backups — from £2/month.
View WordPress hosting plans →