A Strange Problem with Custom CSS

Tutrix

I use a lot of CSS code for my forum’s design and have created the “smart-button-community” folder under /assets/extensions/ for this purpose. The “smart-button-community.css” file in that folder works fine.
I was also able to update a local version (XAMPP) of my forum to version 2.0.0-rc.8 without any issues. Before doing so, I removed custom CSS, my own scripts, and incompatible extensions.

When I try to do this on the live version, the process fails when I remove the custom CSS. As soon as I remove the CSS file or the folder, the page stops working.

An error occurred while loading this page.

The log file contains the following error:

[2026-09-02T14:38:56.780109+00:00] flarum.ERROR: InvalidArgumentException: File not found at path: /var/www/vhosts/.............................../smart-button-community.de/httpdocs/assets/extensions/smart-button-community/smart-button-community.css in /var/www/vhosts/.............................../smart-button-community.de/httpdocs/vendor/flarum/core/src/Frontend/Compiler/Source/FileSource.php:24

The file isn’t linked anywhere on my end.

The update runs without any problems here as well—that is, version 2.0.0-rc.8 is installed. But I can’t access the page.

ClaudiusH

Did you ever try to creating a barebone extension for your community that only ships this styling? Just wondering if that might be the cleaner route than manually fiddling around in that asset/extensions folder.
Did you check folder and file permissions after the upgrade? Maybe the content of that folder is now more tightly controlled?

Tutrix

ClaudiusH
As mentioned, the problem already occurs in version 1.8.9. If I remove my CSS file, the page no longer works.

Put the CSS back in, and the page works.

Actually, after removing the CSS, Flarum’s default design should appear and the page should continue to function. That’s how it worked on my local version.

I went ahead and updated the live site anyway, and the update completed without errors. According to composer.json, all extensions have been updated to 2.0.0-rc.8. However, the error persists, and even adding the CSS adapted for 2.0.0-rc.8 doesn’t help.

Currently, everything has been rolled back to version 1.8.19.
What I’m wondering is why Flarum is searching for this custom CSS.
I haven’t added a link to this CSS anywhere.

Karl

Can you share your php flarum info?
Let's try and get this resolved for you ASAP.

Tobi

You might be calling the css file via an extend or problem could come from cache. If you're using Litespeed cache, try to check inside lscache folder (its on backend) and delete all files and folders.

The important thing is that Flarum's frontend compiler has an extension asset registered somewhere, so deleting the physical CSS file does not remove the reference to it. The reference could be in the extension's PHP code, composer.json, an enabled extension record/configuration, or another custom extension.

The command I would run first

This searches essentially everything under the hosting vhosts while ignoring binary files.

If you want the fastest diagnostic path, run these in this order:

grep -Rni --exclude-dir=storage "smart-button-community.css" .

grep -Rni --exclude-dir=storage "smart-button-community" .

grep -Rni --include="*.php" --exclude-dir=storage "smart-button-community" extensions/ vendor/

grep -Rni --include="*.json" "smart-button-community" .

php flarum extension:list | grep -i "smart-button-community"

The key thing we're looking for is something resembling:

$assets->addFile('extensions/smart-button-community/smart-button-community.css');

or:

->css('extensions/smart-button-community/smart-button-community.css')

or another extension explicitly adding that file to Flarum's frontend asset collection.

Tutrix

First, the current php flarum info

Flarum core: 1.8.19
PHP version: CLI: 8.4.24, Web: unable to detect
PHP memory limit: CLI: 512M, Web: unable to detect
MySQL version: 8.4.11
Loaded extensions: Core, date, libxml, openssl, pcre, zlib, bcmath, bz2, calendar, ctype, dba, dom, json, fileinfo, filter, ftp, gettext, gmp, hash, iconv, SPL, mbstring, pcntl, session, standard, Phar, posix, random, readline, Reflection, exif, shmop, SimpleXML, soap, sockets, sysvmsg, sysvsem, sysvshm, tokenizer, xml, xmlreader, xmlwriter, zip, mysqlnd, cgi-fcgi, imagick, curl, gd, mysqli, PDO, pdo_mysql, xsl, sqlite3, intl, sodium, ldap, tidy, imap, pdo_pgsql, pdo_sqlite, igbinary, redis, ionCube Loader, Zend OPcache
+------------------------------------------+---------+--------+----------------------------------+
| Flarum Extensions                        |         |        |                                  |
+------------------------------------------+---------+--------+----------------------------------+
| ID                                       | Version | Commit | Notes                            |
+------------------------------------------+---------+--------+----------------------------------+
| flarum-suspend                           | v1.8.6  |        |                                  |
| fof-user-directory                       | 1.4.1   |        |                                  |
| flarum-tags                              | v1.8.8  |        |                                  |
| fof-pages                                | 1.0.8   |        |                                  |
| flarum-flags                             | v1.8.2  |        |                                  |
| fof-discussion-views                     | 1.0.0   |        |                                  |
| fof-best-answer                          | 1.7.3   |        |                                  |
| fof-sitemap                              | 2.6.1   |        |                                  |
| flarum-markdown                          | v1.8.1  |        |                                  |
| flarum-likes                             | v1.8.1  |        |                                  |
| flarum-sticky                            | v1.8.3  |        |                                  |
| flarum-approval                          | v1.8.2  |        |                                  |
| fof-forum-widgets-core                   | 1.0.0   |        |                                  |
| flarum-lock                              | v1.8.2  |        |                                  |
| fof-seo                                  | 3.0.6   |        |                                  |
| fof-rich-text                            | 1.0.0   |        |                                  |
| ziiven-post-number                       | v0.1.4  |        | Replaced by linkrobins/post-num  |
| rob006-last-post-avatar                  | 1.3.0   |        |                                  |
| resofire-menu-control                    | v2.0.2  |        |                                  |
| quasimo-tag-sidebar                      | v2.0.21 |        |                                  |
| quasimo-carousel-grids                   | v1.0.1  |        |                                  |
| pianotell-flamoji                        | v1.5.0  |        |                                  |
| nearata-related-discussions              | 1.4.0   |        |                                  |
| nearata-no-self-likes                    | v1.2.1  |        |                                  |
| litalino-top-bar                         | 1.5.1   |        |                                  |
| linkrobins-discussion-banners            | v1.1.2  |        |                                  |
| linkrobins-birdseye                      | v1.7.1  |        |                                  |
| justoverclock-guestengagement            | 1.0.3   |        |                                  |
| isaced-email-verification-switch         | 1.0.1   |        |                                  |
| ianm-html-head                           | 1.2.4   |        |                                  |
| ianm-boring-avatars                      | 1.0.1   |        |                                  |
| huseyinfiliz-sticky-title                | 1.8.3   |        |                                  |
| huseyinfiliz-stickiest                   | 1.0.3   |        |                                  |
| huseyinfiliz-show-password               | 1.0.0   |        |                                  |
| huseyinfiliz-modern-footer               | v1.1    |        |                                  |
| huseyinfiliz-leaderboard                 | 1.0.0   |        |                                  |
| gradba-pagination                        | v1.1.1  |        |                                  |
| forumaker-magicbb                        | 1.4.4   |        |                                  |
| fof-usercard-stats                       | 1.0.0   |        |                                  |
| fof-user-bio                             | 1.4.3   |        |                                  |
| fof-upload                               | 1.9.0   |        |                                  |
| fof-terms                                | 1.5.0   |        |                                  |
| fof-subscribed                           | 1.1.5   |        |                                  |
| fof-signature                            | 1.0.0   |        |                                  |
| fof-reactions                            | 1.4.1   |        |                                  |
| fof-online-users-widget                  | 1.0.0   |        |                                  |
| fof-nightmode                            | 1.6.0   |        |                                  |
| fof-news-widget                          | 1.0.0   |        |                                  |
| fof-move-posts                           | v1.1.1  |        |                                  |
| fof-masquerade                           | 2.1.8   |        |                                  |
| fof-linguist                             | 1.1.6   |        |                                  |
| fof-impersonate                          | 1.2.0   |        |                                  |
| fof-forum-statistics-widget              | 1.3.2   |        |                                  |
| fof-formatting                           | 1.1.2   |        |                                  |
| fof-disposable-emails                    | 1.0.0   |        |                                  |
| fof-cookie-consent                       | 1.1.3   |        |                                  |
| fof-blog                                 | 1.0.1   |        |                                  |
| fof-badges                               | 1.0.5   |        |                                  |
| fof-anti-spam                            | 1.1.5   |        |                                  |
| flectar-fancybox                         | 2.3.0   |        |                                  |
| flarum-subscriptions                     | v1.8.1  |        |                                  |
| flarum-statistics                        | v1.8.1  |        |                                  |
| flarum-nicknames                         | v1.8.3  |        |                                  |
| flarum-mentions                          | v1.8.6  |        |                                  |
| flarum-lang-german                       | 1.25.29 |        |                                  |
| flarum-extension-manager                 | v1.0.8  |        |                                  |
| flarum-emoji                             | v1.8.1  |        |                                  |
| flarum-com-tags-under-discussion         | 1.1.0   |        |                                  |
| flarum-bbcode                            | v1.8.0  |        |                                  |
| ffans-clipboardjs                        | v1.1.0  |        | Replaced by linkrobins/clipboard |
| datlechin-silent-edit                    | v0.1.0  |        |                                  |
| datlechin-signup-button                  | v0.1.1  |        |                                  |
| datlechin-link-preview                   | v1.6.1  |        |                                  |
| datlechin-discussion-overview            | v0.3.0  |        |                                  |
| clarkwinkelmann-popular-discussion-badge | 1.1.1   |        |                                  |
| clarkwinkelmann-likes-received           | 1.0.2   |        |                                  |
| blomstra-sort-order-toggle               | 0.2.0   |        |                                  |
| acpl-mobile-tab                          | 1.4.6   |        |                                  |
+------------------------------------------+---------+--------+----------------------------------+
Base URL: https://smart-button-community.de
Installation path: /var/www/vhosts/...../smart-button-community.de/httpdocs
Queue driver: sync
Session driver: file
Scheduler status: Aktiv
Mail driver: smtp
Debug mode: off

Tutrix

Tobi
Thank you very much👍 ; I found it in extend.php.

<?php

/*
 * This file is part of Flarum.
 *
 * For detailed copyright and license information, please view the
 * LICENSE file that was distributed with this source code.
 */

use Flarum\Extend;

return [
        (new Extend\Frontend('forum'))
        ->css(__DIR__.'/assets/extensions/smart-button-community/smart-button-community.css'),
];

I'm now trying to update to version 2.0.0-rc.8.

Tobi

I had a hectic day like that myself once. I spent almost the entire day with a barely usable site, trying to solve an issue where I was absolutely sure the file had been deleted, yet somehow Flarum kept looking for it and I couldn’t figure out where the reference was coming from. After learning these tricky command-line methods for searching through an entire codebase, I finally found the solution. I swore I would never forget those commands again.

Tutrix

Tobi
Now that I've found it thanks to your help, I suspect I must have added it there myself. 🙃

The site is now running version 2.0.0-rc.8 without any problems. I just need to make a few adjustments. 😉