AssertionError: CSS must be nested under a category.

Problem/Motivation

After activating the theme, clearing the cache, I go to the front page and see:

The website encountered an unexpected error. Try again later.

AssertionError: CSS must be nested under a category. See https://www.drupal.org/node/2274843. in assert() (line 198 of core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php).

Drupal\Core\Asset\LibraryDiscoveryParser->buildByExtension() (Line: 87)
Drupal\Core\Asset\LibraryDiscoveryCollector->getLibraryDefinitions() (Line: 66)
Drupal\Core\Asset\LibraryDiscoveryCollector->resolveCacheMiss() (Line: 149)
Drupal\Core\Cache\CacheCollector->get() (Line: 166)
Drupal\Core\Asset\LibraryDiscoveryCollector->getLibrariesByExtension() (Line: 173)
Drupal\Core\Asset\LibraryDiscoveryCollector->getLibraryByName() (Line: 68)
Drupal\Core\Asset\LibraryDependencyResolver->doGetDependencies() (Line: 41)
Drupal\Core\Asset\LibraryDependencyResolver->getLibrariesWithDependencies() (Line: 132)
Drupal\Core\Asset\AssetResolver->getLibrariesToLoad() (Line: 191)
Drupal\Core\Asset\AssetResolver->getCssAssets() (Line: 288)
Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAssetLibraries() (Line: 132)
Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAttachments() (Line: 97)
Drupal\big_pipe\Render\BigPipeResponseAttachmentsProcessor->processAttachments() (Line: 45)
Drupal\Core\EventSubscriber\HtmlResponseSubscriber->onRespond() (Line: 246)
Symfony\Component\EventDispatcher\EventDispatcher::Symfony\Component\EventDispatcher\{closure}() (Line: 206)
Symfony\Component\EventDispatcher\EventDispatcher->callListeners() (Line: 56)
Symfony\Component\EventDispatcher\EventDispatcher->dispatch() (Line: 216)
Symfony\Component\HttpKernel\HttpKernel->filterResponse() (Line: 204)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 32)
Drupal\big_pipe\StackMiddleware\ContentLength->handle() (Line: 116)
Drupal\page_cache\StackMiddleware\PageCache->pass() (Line: 90)
Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 53)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 715)
Drupal\Core\DrupalKernel->handle() (Line: 19)

Steps to reproduce

install D11
install Gin admin theme and activate it for the admin
install aspiration
go to the front page