Hi Rene,

Well, for the sticky option we use two headers, one for normal and one for sticky, so they swap quickly. You can create both headers with template and assign them to the page settings or the customizer, you can reduce their height as you wish.

But, if you want to keep the same header sticky all the time, then disable the sticky option and enter the following Custom CSS.

.l-primary-header--default-wrapper {
    position: fixed;
    left: 0;
    width: 100%;
    top: 0;
}

To reduce the size after scroll, first install the following plugin, it will allow you to place scripts. https://wordpress.org/plugins/insert-headers-and-footers/

Add the following script in head or footer on the settings of plugin.

<script>
$(document).ready(function(){
    $(window).scroll(function(){
        if ($(window).scrollTop() > 100){
            $('.l-primary-header--default-wrapper').css('height', '50px');
        }
    });
});
</script>

To add bottom border, simply add.

.l-primary-header--default-wrapper {
    border-bottom: 1px solid #f3f2f1;
}

Feel free to ask for anything you need.

Kind Regards

Good to know, you are welcome anytime, feel free to ask for anything you need

If you like our theme, please leave us a rate with 5 stars at ThemeForest, that would help us a lot.

Well, the mobile menu is different and it has a different selectors. The selector is the below:

.l-primary-header--responsive-wrapper

Kind Regards,
NeuronThemes