Get the values of properties in CSS using the calc() property. You can try to run the following code to implement the calc() function in CSS
Example
<!DOCTYPE html>
<html>
<head>
<style>
#demo {
position: absolute;
width: calc(100% - 100px);
background-color: blue;
text-align: center;
}
</style>
</head>
<body>
<h1>Heading One</h1>
<div id = "demo">This is it!</div>
</body>
</html>