#header { background-color: #eee; font-weight: normal; margin:0; padding:10px; font-size: small }
hr { margin-top: 20px; }
pre { text-align: left; overflow: visible }
code { background-color: #ffc }
pre code { background-color: #eee }
.pics {position:relative;z-index:0;height:138px;width:580px; text-align:center;}
.pics img {position:absolute; margin:auto;} 

.pics img{
display: none;
}
.pics img:first{
display: block;
}