Want to use same design theme on multiple websites? Well Google's John Mueller said it is okay to do that. in fact he said many sites share the same or similar theme.
The question is named "Does Code Repetition Affect SEO I Used My Domain" A "CSS classes in Domain" B "is there any negative impact on our SEO website?" John replied "No" which means, it's good to do this, it won't hurt you in Google search.
I asked for more clarification and he repeated his question Actually do I create a WordPress theme and can I use it on many websites? John then responded to the quote Many sites use the same themes, which means everything is fine.
Here are the tweets:
Also, Google has mentioned themes in the past saying that changing themes is not harmful but later said that changing themes can affect levels depending on what has been changed.
Forum discussion on Twitter.