html{
	/* background: url('images/presentation.png') no-repeat; */
} 
@media only screen and (max-width:1080px) {
	nav{
		margin-top: 24px;
		border-bottom: 1px #666 solid;
		border-top: 1px #666 solid;
	}
	
	#arborescence{
		margin-top:0px;
		margin-left:0px;
	}
	
}