<div class="container">
  <p>The following element has circular corners.</p>
  <div class="element element-1">
    border-radius: 50px;
  </div>
  <p>The following element has elliptical corners.</p>
  <div class="element element-2">
    border-radius: 100px / 50px;
  </div>
  <p>The following element has equal height and width and a 50% border radius, so it has a circular shape.</p>
  <div class="element element-3">
    border-radius: 50%;
  </div>
  <p>The following element has non-equal height and width and a 50% border radius, so it has an elliptical shape.</p>
  <div class="element element-4">
    border-radius: 50%;
  </div>
  <p>This next example has an asymmetrical look.</p>
  <div class="element element-5">
    border-radius: 50% 30% / 50% 50%;
  </div>
</div>
body {
  background-color: #F5F5F5;
  color: #555;
  font-size: 1.1em;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

.container {
  margin: 20px auto 0;
  width: 90%;
}

.element {
  text-align: center;
  font-size: 1em;
  margin: 0px auto 50px;
  color: white;
  line-height: 200px;
  height: 300px;
  width: 300px;
  font-size: 0.8em;
  background-color: #eb6f86;
}

.element-1 {
  border-radius: 50px;
  position: relative;
}
/* for demonstration purposes only, not needed for the border radius demo */

.element-1:before {
  display: block;
  box-sizing: border-box;
  content: "border radius: 50px";
  width: 100px;
  line-height: 1;
  height: 100px;
  font-size: .7em;
  border-radius: 50px;
  border: 2px solid black;
  text-align: center;
  padding-top: 35px;
  position: absolute;
  bottom: 0;
  right: 0;
}

.element-2 {
  border-radius: 100px / 50px;
  position: relative;
}
/* for demonstration purposes only, not needed for the border radius demo */

.element-2:before {
  display: block;
  box-sizing: border-box;
  content: "border radius: 100px/50px";
  width: 200px;
  height: 100px;
  font-size: .7em;
  border-radius: 100px/50px;
  border: 2px solid black;
  text-align: center;
  padding-top: 30px;
  line-height: 1;
  position: absolute;
  bottom: 0;
  right: 0;
}

.element-3 {
  border-radius: 50%;
}

.element-4 {
  border-radius: 50%;
  height: 200px;
}

.element-5 {
  border-radius: 50% 30% / 50% 50%;
}