How to change Cover Page Background Image On Mobile

Site URL: https://sprout-cinnamon-nygl.squarespace.com/coming-soon?noredirect

Is there a way yo change the background image on a cover page on mobile. 

I am trying to use this CSS to target the image id for the background but it doesn't seem to work.

@media only screen and (max-width: 600px) {
img#yui_3_17_2_1_1638408171512_197{
	content:url('https://static1.squarespace.com/static/6019e8a70f3f30673741f042/t/61a81fb24ebbca75aa73707f/1638408115876/IMG_5123.JPG') !important;
}
}

Any help or guidance is appreciated.

Website: https://sprout-cinnamon-nygl.squarespace.com/coming-soon?noredirect

Password: Transform

Code in Design > Custom CSS won't run on Cover Page

Add this to Cover Page Header

<style>
  @media screen and (max-width:767px) {
  div.sqs-slice-gallery-item.content-fill img {
    visibility: hidden;
}
div.sqs-slice-gallery-item.content-fill {
    background-image: url(https://cdn.pixabay.com/photo/2021/11/11/20/49/sauerland-6787215__340.jpg);
    background-repeat: no-repeat;
    background-size: cover;
}
  }
</style>