body { margin: 0px; overflow: hidden; }
.arrow { position: absolute; background: none; width: 3em; height: 3em; }
#uArrow { top:0px; width: 100%; }
#dArrow { bottom:0px; width: 100%; }
#lArrow { left:0px; height: 100%; }
#rArrow { right:0px; height: 100%; }