In my theme's libraries.yml file, after the global-styling section, i'm trying to replace one JavaScript file from the core Toolbar module (it's addition of padding-top to body interferes with our theme, so just changing that to margin-top).
libraries-override:
toolbar/toolbar:
js:
js/views/BodyVisualView.js: js/views/BodyVisualView.js
I repeatedly get the error:
Drupal\Core\Asset\Exception\IncompleteLibraryDefinitionException: Incomplete library definition for definition 'libraries-override' in extension 'mythemename' in Drupal\Core\Asset\LibraryDiscoveryParser->buildByExtension() (line 93 of /vagrant/web/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php).