#slider {width: 400px; height: 200px; border: 5px solid red; }
.slide {width: 400px; height: 200px; font-size: 40px; background: #eee; position: absolute; z-index: 0; }
#slider .visible {z-index: 100; }
#slider-left, #slider-right {z-index: 1000; position: relative; display: inline-block; width: 50px; height: 50px; background: black; opacity: .3; font-size: 40px; color: white; cursor: pointer; }
#slider-left {float: left; }
#slider-right {float: right; }