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Default Files (folder)
style.css (optional)
icons (optional folder for icons that can be used in css, from custom modul and application.xml)
fonts (optional folder for fonts that can be used in css)
storageConfig.xml (optional, see https://graebert.atlassian.net/l/c/cwGm3Sy5 )
See https://graebert.atlassian.net/wikil/xc/NABNRQ2JZdqwHo section for details about what can be customized and how to do it.