Custom Overrides for CSS file can't be found?

Problem/Motivation

On a relatively clean new install of Drupal 10.2, I got this error:

Warning: file_get_contents(themes/contrib/paxton/css/parallax-slider-custom-overrides.css): Failed to open stream: No such file or directory in Drupal\system\Controller\CssAssetController->generateHash() (line 43 of core/lib/Drupal/Core/Asset/AssetGroupSetHashTrait.php).
Warning: file_get_contents(themes/contrib/paxton/css/paxton-custom-overrides.css): Failed to open stream: No such file or directory in Drupal\system\Controller\CssAssetController->generateHash() (line 43 of core/lib/Drupal/Core/Asset/AssetGroupSetHashTrait.php).

When I go to the directory, I see only:

root@XXX:/var/www/XXX.XXX/XXX/web/themes/contrib/paxton/css# ls
fancybox.css              font-awesome.min.css  glyphicons.css  hover.css  parallax-slider.css  style.min.css
font-awesome-ie7.min.css  fonts                 halflings.css   page.css   social-icons.css

Installation was directly from composer.

Any thoughts?

TIA.