Ask HN: Where/how to get the 'typical startup website' theme?

Are all startup websites based on a certain theme? If so,is there a way to easily build sites like it or are they all just built custom on a framework like bootstrap?

Some examples of what I mean:

https://www.quivee.com/

http://sendgrid.com/

http://www.mashery.com/

http://www.twilio.com/

https://trychec.com/

http://cropup.com/

And a ton more!

They're all different, but they seem to share the same underlying theme.