#bar {
    background:silver;
    height:32px;
    }

.dropdown {
    background:lightblue;
    width:50%;
    float:left;
}

.box {
    height:32px;
    background:orange;
    }

.boxdown {
    background:red;
    display:none;
}

.boxdown .box {
    background:darkorange;
}

.dropdown:hover .boxdown {
    display:block;
}