A client reported a broken mobile layout across multiple pages after activating WP Rocket’s Remove Unused CSS (RUCCS) feature. The issue was traced to RUCCS removing media query styles from the site’s child theme stylesheet, which caused responsive styles to disappear. Here’s how the Freshy team diagnosed and resolved the issue.
Issue background
The issue appeared on several front-end pages, where mobile layouts were collapsing or losing key style elements. This typically presented as:
- Unaligned or overlapping page elements on mobile
- Missing padding or spacing defined in
@mediaCSS queries - Desktop layout rules applying across all breakpoints
The problem was specific to mobile devices and appeared after WP Rocket’s “Remove Unused CSS” optimization was enabled.
Diagnosis
Our developer began by reviewing the affected pages and confirming the behavior on both desktop and mobile.
Affected URLs included:
- /services/urgent-care/lab-testing
- /for-employers/medication-alcohol-testing
The team first verified that caching wasn’t the root cause, then inspected the generated CSS files produced by WP Rocket’s Remove Unused CSS feature.
Upon inspection, it became clear that media query rules (e.g., @media (max-width: 768px)) were being removed from the site’s child theme stylesheet (style.css).
This meant that all responsive styling was stripped out, causing mobile versions to render using only desktop selectors.
Further research into WP Rocket’s documentation and user community confirmed this as a known issue: RUCCS prioritizes desktop selectors and can remove responsive CSS when it determines them as “unused” during its static crawl.
Resolution steps
To resolve this issue while maintaining performance benefits from WP Rocket, the following fix was implemented:
- Exclude the child theme stylesheet from RUCCS
Navigate to WP Rocket → File Optimization → CSS Files → Remove Unused CSS.
In the Exclusion list, add:/wp-content/themes/[your-child-theme]/style.cssSave and clear the cache.
- Regenerate the CSS cache
Run “Clear and Regenerate CSS/JS Files” from WP Rocket to ensure new CSS files were created without stripping responsive styles. - Validate on mobile
Test all key pages on multiple devices and viewport sizes using browser DevTools’ mobile view to confirm that responsive layout styles were restored.
Final outcome
After excluding the child theme’s CSS file, all responsive styling returned to normal, resolving the broken mobile layout without sacrificing overall page speed.
The RUCCS feature remains active for other assets, allowing WP Rocket to continue optimizing unused CSS across third-party plugins and themes.
Technical takeaway
If your site uses custom or child theme CSS, it’s crucial to exclude the main stylesheet from RUCCS to prevent mobile layouts from breaking.
This issue primarily occurs when:
- CSS files contain nested
@mediaqueries - RUCCS cannot detect mobile breakpoints during its scan
- Custom styles are defined in a file that doesn’t load directly on the initial desktop render
By strategically using the exclusion list, you can keep WP Rocket’s optimization benefits while protecting responsive design integrity.
Need help fixing similar issues?
If you’re experiencing layout breakage or mobile responsiveness problems after enabling WP Rocket or another optimization plugin, Freshy’s WordPress experts can help identify and resolve the root cause.
Contact Freshy today to get expert support.
