.a{ width:0pxheight:0pxmargin:autoborder-bottom:20px solid #f00border-left:40px solid #fffborder-right:40px solid #fff}
.b{ width:0pxheight:0pxmargin:autoborder-top:20px solid #f00border-left:40px solid #fffborder-right:40px solid #fff}
</style>
<div class="a"></div>
<div class="b"></div>
用margin可以。因为margin可以设为负值
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html charset=utf-8" />
<title>无标题文档</title>
<style>
.img-div { background:#ccc width:200px}
.img-div img.margin-t{ margin-top:-30px}
.img-div img.margin-l{ margin-left:32px}
</style>
</head>
<body>
<div class="img-div">
<img src="img.png" /><img src="img.png" /><img src="img.png" />
<img src="img.png" class="margin-t margin-l" /><img src="img.png" class="margin-t"/>
<img src="img.png" class="margin-t"/><img src="img.png" class="margin-t" /><img src="img.png" class="margin-t"/>
<img src="img.png" class="margin-t margin-l"/><img src="img.png" class="margin-t" />
<img src="img.png" class="margin-t"/><img src="img.png" class="margin-t" /><img src="img.png" class="margin-t"/>
</div>
</body>
</html>
附件就是例子,你可以直接看效果。