Assets 

Filename

assets.yml

Root Node

assets

The assets.yml file used to load Sass and CSS files. The input files will be automatically merged to a single output file and optimized for web presentation.

src/Acme/Bundle/DemoBundle/Resources/config/oro/assets.yml 
assets:
    css:
        inputs:
            - acmedemo/path/to/css/first.scss
            - acmedemo/path/to/css/second.scss
            - acmedemo/path/to/css/third.css
            # You can import Sass modules from node_modules.
            # Just prepend them with a ~ to tell Webpack that this is not a relative import.
            # See: https://webpack.js.org/loaders/sass-loader/#resolving-import-at-rules
            - '~prismjs/themes/prism-coy.css'
        auto_rtl_inputs:
            # List of file masks for inputs that has to be processed with RTL plugin
            - 'acmedemo/path/**'

To apply changes, run the following command that installs and builds application assets:

php bin/console oro:assets:install  --symlink