Use the CSS user-select property to set whether the text of the element can be selected or not with CSS
Example
<!DOCTYPE html>
<html>
<head>
<style>
div {
user-select: none;
}
</style>
</head>
<body>
<h2>This is demo heading</h2>
<div>This is demo text. You won't be able to select it.</div>
</body>
</html>