Indeed, it is entirely feasible to create a dropdown menu without the use of Javascript, as long as the dropdown automatically appears when hovering over a button. One popular method is the implementation known as "Son of suckerfish," which incorporates minimal Javascript for older browser support. While I have not personally utilized this technique for a standalone button, achieving this functionality should be relatively straightforward.
To my understanding, creating a dropdown menu that responds to clicks cannot be accomplished through CSS alone.
Upon further reflection, I must admit I am uncertain about the specific aspect you are referring to. Are you inquiring about the visual appearance of the button or the interactive nature of a dropdown button?