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?<p>Some examples of what I mean:<p>https://www.quivee.com/<p>http://sendgrid.com/<p>http://www.mashery.com/<p>http://www.twilio.com/<p>https://trychec.com/<p>http://cropup.com/<p>And a ton more!<p>They're all different, but they seem to share the same underlying theme.