render_example.libraries.yml

# Define a new asset library which includes the CSS used to style the page
# at examples/render_example/arrays. See how asset libraries are attached to
# render arrays by reading the example code in
# Drupal\render_example\Controller\RenderExampleController::arrays().
render-example.library:
  version: 1.x
  css:
    theme:
      css/render_example.css: {}