Your pages download styling rules that they never actually apply. Like unused JavaScript, this adds unnecessary weight your visitors' browsers have to carry before your page becomes usable.
On WordPress
The Asset CleanUp or WP Rocket plugin can disable specific stylesheets on pages that don't use them. WooCommerce and popular page builders are common sources of large unused CSS — you can disable their styles on non-shop or non-builder pages.
On Shopify
Shopify themes sometimes include CSS for every section type even on pages that only use a few. If you're comfortable with theme development, removing unused theme sections reduces the CSS loaded. Otherwise, focus on removing unused apps.
Pro tip: Page builder plugins (Elementor, Divi, Beaver Builder) load their entire design framework CSS on every page. If you only use the builder on some pages, disabling its stylesheet on pages built with standard WordPress blocks can remove hundreds of kilobytes of unused CSS.
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