How to make the gallery in Squarespace under the header, fit the height of the section block?

Hi, I am adjusting the homepage of our site. On top of our site we want a full size gallery block with changing images just under our header. I am new to Squarespace. I've managed to insert some codes already but nothing works. 

The image block fits to the full section height but a gallery block leaves a whitespace block underneath. Especially on Mobile setting and smaller screen size. 

Is there a way to get the gallery to full section height responsive to all different settings? Would love your help!

What is page url? We can check easier

www.cloudibkk.com

I think i managed to change that, but lacking the margin, the section now lost on height. Can you suggest how to increase it?

44 minutes ago, cloudibkk said:

www.cloudibkk.com

I think i managed to change that, but lacking the margin, the section now lost on height. Can you suggest how to increase it?

What is access password?

CLOUDITEMPORARY

the margins have reverted back to what they were. Even when I inspect they remain at 0 but something happens and all comes back to what it was despite changes. 

Same with the white background color first box under header for text on the Delivery Menu page. I added in the CSS the code and changed it. It came up alright but after save and refresh it keeps changing back to without background. 

On 4/2/2022 at 4:04 PM, cloudibkk said:

the margins have reverted back to what they were. Even when I inspect they remain at 0 but something happens and all comes back to what it was despite changes. 

Same with the white background color first box under header for text on the Delivery Menu page. I added in the CSS the code and changed it. It came up alright but after save and refresh it keeps changing back to without background. 

Did you solve? It looks fine to me