To set the responsive font size, use the ‘viewport width’ and set it to ‘vw’ unit. You can try to run the following code to use ‘vw’ unit −
Example
<!DOCTYPE html>
<html>
<head>
<style>
h1 {
font-size:8vw;
}
</style>
</head>
<body>
<h1>This is demo heading</h1>
<p>This is demo text.</p>
</body>
</html>