Hi Ingo,
Thank you for reaching out to us. In X you can do it with custom scripting, try adding the following code in the Theme Options > JS:
jQuery(document).ready(function($){
$(window).scroll(function(){
if ($(this).scrollTop() > 100) {
$('body.x-navbar-fixed-top-active .x-navbar-wrap').css("height", "60px");
$('.x-navbar-inner').css("min-height", "60px");
$('.x-brand img').css("width", "90px");
$('.x-navbar .desktop .x-nav > li > a').css({"padding-top": "35px", "height": "60px"});
} else {
$('body.x-navbar-fixed-top-active .x-navbar-wrap').css("height", "120px");
$('.x-navbar-inner').css("min-height", "120px");
$('.x-brand img').css("width", "130px");
$('.x-navbar .desktop .x-nav > li > a').css({"padding-top": "70px", "height": "120px"});
}
});
});
Please note that the code provided above serves as a guide only and is to help you in getting started so implementing it and maintaining the code will be out of our support scope and for further maintenance for new possible versions of the theme that may cause the customization to break, you will need to hire a developer.
Thanks!