#b {
background: orange;
box-shadow: 0 0 10px black;
z-index: 2;
position: relative;
}
#c {
background: red;
z-index: 1;
position: relative;
}
ul {
list-style: none;
margin: 0;
padding: 0;
z-index: 1;
position: relative;
}
li {
display: inline-block;
padding: 2px 5px;
}
.current {
background-color: orange;
z-index: 3;
position: relative;
}
#d {
box-shadow: 0 0 10px black;
z-index: 2;
}
<div id="a">
<div id="b">bbb</div>
<div id="c">
<ul>
<li>a</li>
<li class="current">b</li>
<li>c</li>
<li>d</li>
</ul>
</div>
</div>
<div id="d">dddd
</div>
See Question&Answers more detail:os