Hi. Your template doesn't have "shrink" class name when scrolling. You need to use JS code to add this class.
Add this to Settings > Advanced > Code Injection > Footer
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script>
$(function(){
var visibleTop = 30;
$(window).scroll(function() {
var scroll = getCurrentScroll();
if ( scroll >= visibleTop ) {
$('header#header').addClass('header-sticky');
}
else {
$('header#header').removeClass('header-sticky');
}
});
function getCurrentScroll() {
return window.pageYOffset || document.documentElement.scrollTop;
}
});
</script>
<style>
header#header img {
transition: all 0.3s;
}
header#header.header-sticky img {
max-height: 50px;
transition: all 0.3s;
}
</style>