Smooth scroll header with fixed position

Question

How to create smooth scroll when I change the position to fixed. I try to add the animation but it does not work. Better use jquery animation();

Answer 1

You can use @keyframes to add some transition effects to the scroll.

$(window).scroll(function() {
  var sticky = $('.mobile-menu'),
    scroll = $(window).scrollTop();
   
  if (scroll >= 40) { 
    sticky.addClass('fixed'); }
  else { 
   sticky.removeClass('fixed');

}
});

header {
  padding: 20px 40px;
  background: gray;
  width: 100%;
  
  -webkit-transition: all 0.5s ease;
  -moz-transition: position 10s;
  -ms-transition: position 10s;
  -o-transition: position 10s;
  transition: all 0.5s ease;
}
section {
  height: 150vh;
}


.fixed {
  position: fixed;
  top: 0;
  left: 0;
  animation: smoothScroll 1s forwards;
}
@keyframes smoothScroll {
	0% {
		transform: translateY(-40px);
	}
	100% {
		transform: translateY(0px);
	}
}

Text here
Sugar plum muffin cookie pastry oat cake icing candy canes chocolate. Gummi bears chupa chups fruitcake dessert jelly. Muffin cookie ice cream soufflé pastry lollipop gingerbread sweet. Unerdwear.com bonbon candy marzipan bonbon gummies chocolate cake
  gummi bears powder. Unerdwear.com tart halvah chocolate cake dragée liquorice. Sugar plum chocolate bar pastry liquorice dragée jelly powder. Jelly tootsie roll applicake caramels. Marzipan candy tootsie roll donut. Gummies ice cream macaroon applicake.