Position:fixed is the right answer, but beware: not every device has a PC sized screen. The minimum you are likely to need to support is 360px or so. So floating the buttons, say, 400px from the top is a no no. Try something like
#leftbuttons:
position: fixed;
left: 0;
width: 150px;
top: auto;
bottom: auto;
I haven't tested it, but that should be something like what you need...
