<!doctype HTML>
<style>
.outer {
position:relative;
width: 120px;
height: 120px;
border-radius: 40px;
background-color: rgba(255,0,0,0.5);
}
.inner {
position:absolute;
top:10px;
left:10px;
width: 100px;
height: 100px;
border-radius: 30px;
background-color: lightblue;
}
</style>
<div class = "outer">
<div class = "inner"></div>
</div>