The fastest way would be load in jQuery and insert this snippet.
Step 1: Insert jQuery script tag before the closing body
tag (</body>
)
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
Step 2: Insert this snippet below
<script>
// Bind all a href clicks to this function
$(document).on('click', 'a', function(event){
// Prevent default events
event.preventDefault();
// Animate the body (html page) to scroll to the referring element
$('html, body').animate({
scrollTop: $( $.attr(this, 'href') ).offset().top
}, 1000);
});
</script>
You can edit where it says 1000
to change the speed and you can also add or subtract scrollTop: $( $.attr(this, 'href') ).offset().top
to get additional offset off your element.
Example: This will be 100 pixels above your element instead of exactly on top.
scrollTop: $( $.attr(this, 'href') ).offset().top - 100