#container {
width: 100px;
height: 100px;
position: relative;
}
#navi,
#infoi {
width: 100%;
height: 100%;
position: absolute;
top: 0;
left: 0;
}
#infoi {
z-index: 10;
}
<div id="container">
<div id="navi">a</div>
<div id="infoi">
<img src="https://appharbor.com/assets/images/stackoverflow-logo.png" height="20" width="32" />b
</div>
</div>
我建议使用来了解position: relative
和子元素position: absolute
。