task-03.css

#parent{
   width:400px;
   height: 200px;
   background-color: #ccc;
   position: absolute;
   top: 50%;
   left: 50%;
   margin: -100px 0 0 -200px;
}
#child1 {
  width: 50px;
  height: 50px;
  background-color: #fc0;
  border-bottom-right-radius: 100%;
  position: absolute;
}
#child2 {
  width: 50px;
  height: 50px;
  background-color: #fc0;
  border-top-left-radius: 100%;
  position: absolute;
  top: 150px;
  left: 350px;
}

task-03.html

<div id="parent">
  <div id="child1"></div>
  <div id="child2"></div>
</div>