<style>
.地球{position:relative;
top:50px;
left:50px;
width:300px;
height:300px;
background-color:#abcdef;
text-align:center;
margin:50px auto;
line-height:50px;}

.月{position:absolute;
top:50px;
left:50px;
width:150px;
height:150px;
color:white;
background-color:dodgerblue;
text-align:center;
line-height:100px;
z-index:0}

.衛星{position:absolute;
top:150px;
left:150px;
width:80px;
height:80px;
color:white;
background-color:#456789;
border-radius:50%;
line-height:84px;
z-index:10;}
</style>

<div class="地球">#abcdef
<div class="月">dodgerblue</div>
<div class="衛星">#456789</div>
</div>