Who is responsible for the looks of the page you're looking at right now and who's responsible for the way the page responds to your clicks?
It is the front-end developer who's responsible for everything that is pleasing to your eyes. The way the site looks, the way effects appear on hovering your cursor is all due to the work of a front-end developer.
It is the back-end developer who's responsible for the code that works on handling the information received, managing data-bases and so much more.