how to make a navigation section fixed position

hi, I'd like to make my website's navigation bar fixed position. could anyone show me how to do it?

here is the page link: https://www.cluedesignstudio.com/gallery

and the image shows the section that I'd like to fix position.

thank you.

Add to Design > Custom CSS

@media screen and (min-width:992px) {
[data-section-id="647634f60a7e117d5b8c8d65"] {
    position: sticky;
    top: 0px;
    z-index: 999999;
    position: -webkit-sticky;
}
}

Hi, thank you very much for your help. I tried to add this custom CSS, but it's not working🙁 not sure if I did it wrong or anything. 

4 hours ago, Yan2233 said:

Hi, thank you very much for your help. I tried to add this custom CSS, but it's not working🙁 not sure if I did it wrong or anything. 

I see it already worked here. Can you check it again?