Is Lido open source?

I've been hearing a lot about Lido lately, and it seems to be quite popular in the cryptocurrency community. However, I'm a bit curious about its origins and development. Could you tell me, is Lido open source? I'm interested in understanding how its codebase is structured and if it's been audited for security vulnerabilities. Additionally, I'd like to know if the community is actively contributing to its development and if there's a transparent process for submitting and reviewing changes. Understanding the openness and transparency of Lido's codebase would greatly assist me in evaluating its trustworthiness and potential.