W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<head>
<style> 
#rcorners1 {
  border-radius: 25px;
  background: #73AD21;
  padding: 20px; 
  width: 200px;
  height: 150px;  
}

#rcorners2 {
  border-radius: 25px;
  border: 2px solid #73AD21;
  padding: 20px; 
  width: 200px;
  height: 150px;  
}

#rcorners3 {
  border-radius: 25px;
  background: url(paper.gif);
  background-position: left top;
  background-repeat: repeat;
  padding: 20px; 
  width: 200px;
  height: 150px;  
}
</style>
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-4638549725433695" crossorigin="anonymous"></script><script src="//www.p2hp.com/tj.js"></script></head>
<body>

<h1>The border-radius Property</h1>

<p>Rounded corners for an element with a specified background color:</p>
<p id="rcorners1">Rounded corners!</p>
<p>Rounded corners for an element with a border:</p>
<p id="rcorners2">Rounded corners!</p>
<p>Rounded corners for an element with a background image:</p>
<p id="rcorners3">Rounded corners!</p>

</body>
</html>