I can copy any website design, even I don't even know how to make a nice looking banner or logo.
Yes and no.
Yes, anyone can copy the design of a website, using the source code of the page they want to copy.
No, if the site template is developed in a more elaborate way, it will make this task more complicated and it will be difficult to make the site look exactly the same. There will be more elements out of place than on a simple website.