Hi Jau,
There used to be the Design Certification that covered the design tools, etc. but that was sunset as it covered the old Design Manager. However, there’s a new Developer Certification on the way and some content is already up.
Here are some details posted by Luke Summerfield from a conversation on the Developers Slack:
Design Cert was retired in September because it was very outdated and basic.
The new CMS for Developers is well underway. There are already 4 lessons live (with the last 2 going live by the end of this month). View them here: HubSpot Login and Sign in
Once all the content is live, the team will create a new practicum and certification criteria. Then we will officially “launch” the new CMS for Developers certification.
I’d estimate end of February / early March for the certification to be available. In the meantime, all the content will be already live and you can get sandbox portals to play in with the Discovery Kit: HubSpot CMS Developer Discovery Kit
The Discovery Kit should also give you access to that Slack 
I hope that helps!
Stephanie O’Gay Garcia
HubSpot Design / Development
If this helped, please mark it as the solution to your question, thanks!