border-radius works on all elements, even images. It's an easy way to make images look great on a webpage.

To round the corners of all images using border-radius, type 100px;.

<head>
<style>
img {
border: solid 5px black;
border-radius: 100px;
}

</style>
<link rel="stylesheet" href="style.css">
</head>
<body>
<h1>Window Seat Digest</h1>
<h3>A collection of views from airplanes</h3>
<img src="https://mimo.app/r/wing1.png">
<img src="https://mimo.app/r/wing2.png">
</body>
</html>]]>

Make sure to type 100px.