Answers for "css on scroll"

smooth scroll css

html {
  scroll-behavior: smooth;
}

/* No support in IE, or Safari
You can use this JS polyfill for those */
http://iamdustan.com/smoothscroll/

css no overflow

div.ex1 {
  overflow: scroll;
}

div.ex2 {
  overflow: hidden;
}

div.ex3 {
  overflow: auto;
}

div.ex4 {
  overflow: visible;
}

scroll down style

<script type="text/javascript">
$window.scrollTop(function(){ 

var a = 112;
var pos = $window.scrollTop();
if(pos > a) {
    $("menu").css({
                position: 'fixed'
            });
}
else {
    $("menu").css({
                position: 'absolute',
                top:'600px'
            });
}
});
</script>