To set the shape of the border of the top-left corner in JavaScript, use the borderTopLeftRadius property. Set the border radius using this property.
Example
You can try to run the following code to learn how to set the shape of the top-left 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 left border radius</button>
<script>
function display() {
document.getElementById("box").style.borderTopLeftRadius = "20px";
}
</script>
</body>
</html>