How can I get my image to pull through in CSS?

.page-header {
  background-image: url("../images/page-header-img.png");
  background-repeat:no-repeat;
  background-size:cover;
  background-position:center;
  width:100% ; 
  height:250px;
  display:block;
  justify-content: center;
  grid-column: 1 /  span 12;
  margin-bottom:1rem;
  background-position: top;
}

<div class="page-header"><h1><?php the_title();?></h1></div>