Unable to reduce margin under header.

Huge space I can't get rid of. 🥵

https://www.adventurehire.com.au/home/book-filter

As is shown in the edit mode, the text box and button are up close to the header.

But when I save and view, regardless of device, there is a huge gap (margin) between the header and the text box and button.  (Squarespace 7.1 with fluid.)

As you can see by the image below, the text box is at the top of the grid.

It looks to me as if the grid is centred on the background and I can't move the grid up higher.

This is the code behind the button, just in case that has some effect on the problem and/or solution.

<div id="#block-yui_3_17_2_6_1459644649106_53673" class="slideUp">

 <script> 

 $(window).scroll(function () {

 $('#block-yui_3_17_2_1_169821492614_1476').each(function () {

 var topOfWindow = $(window).scrollTop(),

 bottomOfWindow = topOfWindow + $(window).height();

 var imagePos = $(this).offset().top;

 if(imagePos <= bottomOfWindow-100 && imagePos >= topOfWindow-250){

 $(this).addClass('slideUp');

 }else{

 $(this).removeClass('slideUp');

 }

 });

 });

 </script>

Any help would be much appreciated.