#contenedor{
 margin:5px auto;
 width:800px;
}
p{
text-align:center;
font-size:30px;
}
li{
 list-style-type:none;
 float:left;
}

#image_holder{
width:750px;
height:755px;
}
.instrumento{
border:2px none yellow;
margin:2px;
width:140px;
}
.instrumento:hover{
 border:2px solid yellow;
 margin:0px;
}
.bg{
left:300px;
display:none;
margin-top:170px;
margin-left:auto;
margin-right:auto;
position:absolute;
}