shinyglass bundles the following third-party files.

inst/fonts/inter/InterVariable-latin.woff2
  Inter, a typeface by Rasmus Andersson.
  Copyright (c) 2016 The Inter Project Authors (https://github.com/rsms/inter)
  Licensed under the SIL Open Font License, Version 1.1.
  The full license is in inst/fonts/inter/OFL.txt.