<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
   <div class="cycle" />
</body>
</html>
.cycle {
  position: relative;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  border: 2px solid #000;
}

.cycle::after {
  font-size: 40px;
  content: '+';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.