Currently, the website does not scroll in chrome

I found a fix for this issue.

html {
    overflow: hidden;
    height: 100%;
}
body {
    height: 100%;
    overflow: auto;
}

However, adding this into the Custom CSS breaks the header background changing as you move down the page on all browsers. It also prevents the Back to Top button from displaying.

I think the issue with the Back to Top button is in the if statement

if ($(this).scrollTop() > $(window).height() *0.7 ) {
 $('.scrolltotop').fadeIn();
 } else {
 $('.scrolltotop').fadeOut();
 }

This is very frustrating and I am unsure what to do to resolve this.