How to add a fixed background image for a certain page only?

Hi, how to add a fixed background image for a certain page only? I've came up with this code but it doesn't work for certain collection. When pasted without the "collection" line, it works, however for all pages equally. How to make it work for a certain page only? Thank you.

#collection-COLLECTIONNUMBER
{

body::before {
  background-image: url('IMAGELINKHERE.JPG');
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
  content: '';
  height: 100%;
  opacity: 1;
  position: fixed;
  left: 0;
  top: 0;
  width: 100%;
  z-index: -10;
}

.page-section,
.page-section .section-background {
  background-color: transparent !important;
}

}

You can add this code to Page Header

<style>
  body::before {
  background-image: url('IMAGELINKHERE.JPG');
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
  content: '';
  height: 100%;
  opacity: 1;
  position: fixed;
  left: 0;
  top: 0;
  width: 100%;
  z-index: -10;
}

.page-section,
.page-section .section-background {
  background-color: transparent !important;
}
</style>