http://appro.mit.jyu.fi/opetusteknologia/luennot/luento4/z-index.css

body {
  background: white none; color: black;
}

.l1 {
  position: absolute;
  z-index: 1;
  top: 5%; left: 5%;
  height: 2.5em;
  background: transparent none; color: yellow;
  font-size: 800%; font-weight: bolder;
  font-family: Impact, Verdana, sans-serif;
}

.l3 {
  position: absolute;
  z-index: 3;
  top: 12%; left: 15%;
  height: 2.5em;
  background: transparent none; color: silver;
  font-size: 800%; font-weight: bolder;
  font-family: Impact, Verdana, sans-serif;
}

.l5 {
  position: absolute;
  z-index: 5;
  top: 19%; left: 25%;
  height: 2.5em;
  background: transparent none; color: blue;
  font-size: 800%; font-weight: bolder;
  font-family: Impact, Verdana, sans-serif;
}

.l1:hover, .l3:hover, .l5:hover {
  z-index: 50;
}