How CSS helps to develop a Responsive Website ?
You can create it with CSS. I recommend you to read about what it is.
As far as I know, CSS is the perfect stylesheet for designing applications. When it comes to designing webites, I prefer using ready-made WP themes. For my current project I've been using on of these wordpress photography website themes https://www.templatemonster.com/cate...dpress-themes/ . They are pretty customizable.