CSS position Pattern

Take a look to this pattern and you will understand how it works. Assign your container position: relative;. There child assign position:absolute;. The absolute elements you can positioning by using top, bottom, left, right.

body {
  background: gray;
} 

.container {  
  position: relative;
  width: 50%;
  height: 100vh;
  border: 3px solid #73AD21;
  margin: 0px auto;
  text-align:center;  
}

.container div {
  padding: 10px;
}

.container div:nth-child(1) {
  background: yellow;
  position: absolute;
  width: 200px;
  height: 200px;  
  top: 50%;
  left: 20%;
}

.container div:nth-child(2) {
  background: green;
  position: absolute;
  width: 100px;
  height: 100px;  
  top: 20%;
  right: 20%;
}

.container div:nth-child(3) {
  background: red;
  position: absolute;
  width: 50px;
  height: 50px;  
  top: 10px;
  right: 10px;  
}

.container div:nth-child(4) {
  background: yellowgreen;
  position: absolute;
  width: 300px;
  height: 30px;  
  top: 10px;
  left: -20px;  
}

<div class="container">
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>FLAG</div>
</div>

DEMO: https://codepen.io/mike-lowrey/pen/BamodMQ