To set the shape of the border of the top-right corner in JavaScript, use the borderTopRightRadius property. Set border radius using this property.
Example
You can try to run the following code to learn how to set the shape of the top-right border with JavaScript.
<!DOCTYPE html>
<html>
<head>
<style>
#box {
border: thick solid gray;
width: 300px;
height: 200px
}
</style>
</head>
<body>
<div id="box">Demo Text</div>
<br><br>
<button type="button" onclick="display()">Change top right border radius</button>
<script>
function display() {
document.getElementById("box").style.borderTopRightRadius = "20px";
}
</script>
</body>
</html>