Actually, the design is The Atlassian Design Guidelines and it uses the Atlassian User Interface project (Atlassians Bootstrap) which all Atlassian products are

Actually, the design is The Atlassian Design Guidelines and it uses the Atlassian User Interface project (Atlassians Bootstrap) which all Atlassian products are using to maintain a consistent look and feel https://developer.atlassian.com/design/ https://developer.atlassian.com/design/