<style>
.menu{width:100%;height:100px;background:#f00;}
.menu .nav{width:120px;height:100px;line-height:100px;text-
align:center;background:#00f;float:left;margin-right:10px;color:#fff;}
</style>
<div class="menu">
<div class="nav">菜单1</div>
<div class="nav">菜单2</div>
<div class="nav">菜单3</div>
<div class="nav">菜单4</div>
<div class="nav">菜单5</div>
<div class="nav">菜单6</div>
</div>
给nav做float:left;向左浮云,这样,当menu这个容器宽度缩小后,浮云就会自动向下排去了。