A Pen by René Meye.

index.html

<div class="container">
  <div class="circle"></div>
</div>

KDldI.markdown

KDldI

A Pen by René Meye on CodePen.

License.

style.css

.container {
  width: 15%;
  background: blue;
}

.circle {
  border-radius: 50%;
  width: 100%;
  padding-bottom: 100%;
  background: white;
}