Q: Hello, can a website expressing an idea be protected under copyright laws?

A: Copyright law does not protect ideas. Copyright would, however, protect the expression of that idea, so the text of the html/css/php are protected. If someone copies a large chuck of your code verbatim, that would likely be copyright infringement. If someone likes the structure of your website, and reverse engineers it on their own, with their own code, that would not be copyright infringement. There is something of a gray area between these two extremes, where someone copies your code then makes some degree of change to it. How much alteration is enough to clear that person of copyright infringement can only be determined by a judge.

To elaborate a bit:

In copyright law, it is clear, for example, that one who copies the exact words of a copyrighted story is copying protected expression. It is less clear, however, whether copyright also extends to the plot and characters of that story. At a high level, elements like plot and character are simply abstract ideas. For example, the idea of a story about a wizard in school is highly abstract. Similarly, the idea of a superhero who can fly is quite abstract.

But elements such as plot and character are not totally ineligible for copyright protection. An infringement claim based on plot and elements will depend on the level of detail which is copies. If the story line of Harry Potter or Superman is copied at a high level of detail, a court is likely to conclude that the accused infringer copied protected expression rather than abstract ideas.

This is known as the "idea/expression dichotomy" in copyright law. Searching around for that term should help you find specific examples of what level of detail is too much.

While an idea is not copyrightable, an expression of an idea is copyrightable. Pages 62-66 of this article in PDF (http://www.rbs2.com/cidea.pdf), by Dr. Ronald Standler, a MA attorney explains this concept a bit further with several examples.