Room's Avatar missing



I am currently creating a RocketChat server.
I think I made a mistake with custom CSS, room’s avatar is missing.
How can I get them back?

Sorry for my bad English.

Server Setup Information

  • Version of Rocket.Chat Server: 3.7.1
  • Operating System: Windows 10 x64
  • Number of Running Instances: 22767
  • DB Replicaset Oplog: Activated
  • NodeJS Version: 12.14.0
  • MongoDB Version: 4.0.20