<html>
<head>
	<meta charset="utf-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<title></title>
	<link rel="stylesheet" href="">
</head>
<body>
  <h3> Dog number <span></span> can talk </h3>
  <h3> Dog number <span></span> is  intelligent </h3>
  <h3> Dog number <span></span> just learned how to swim </h3>
</body>
</html>
body {
    font-family: Arial; 
    counter-reset: dog_number; 
}

h3 span::before {
    counter-increment: dog_number;
    content: counter(dog_number); 
    color: red;
}
Rerun