<div class="box">
   <div class="item"></div>
</div>

.box {
   width:500px;
   height:500px;
   border:5px solid #f00;
   position:relative;
}
.item {
   width:50px;
   height:50px;
   background-color: #f00;
   border-radius:100%;
   position: absolute;
   right:0;
   bottom:100px;
}