<div class="example">
  <div class="circle red"></div>
  <div class="circle blue"></div>
  <div class="circle pink"></div>
</div>
* {
  box-sizing: border-box;
}

*:before, *:after {
  box-sizing: inherit;
}

body {
  width: 100%;
  height: 100%;
  font-size: 100%;
  line-height: 1.5;
}

.example {
  width: 100%;
  height: 100vh;
  max-width: 1200px;
  margin: 0 auto;
  padding: 1em;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.circle {
  width: 100px;
  height: 100px;
  border-radius: 50%;
}

.red {
  background-color: darkred;
}

.blue {
  background-color: lightblue;
}

.pink {
  background-color: darksalmon;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.