*{
	margin:0;
	padding:0;
}
body{
	padding:30px;
}
h1{
	padding:0 0 20px;
}
.slideshow{
	width:300px;
	height:300px;
	margin:0 20px 20px 0;
	float:left;
	position:relative;
}
/* img要素は絶対配置で一か所に重ねる */
.slideshow img{
	position:absolute;
	top:0;
	left:0;
	border: 1px solid #000;
	vertical-align:top;
}

/* 2番目以降のimg要素にclass="alt"を付け、消す */
.slideshow img.alt{
	display:none;
}