There are a few ways to position the background image. You can use the background position property with values that are in pixels, relative positions, and percentages. In PrestaShop, most of the syntaxes used are based on relative position.

As an example, a header link uses top center in this property.

#header_links a {
display: block;
height: 15px;
color: #595a5e;
padding-top: 19px;
text-align: center;
text-decoration: none;
background-repeat: no-repeat;
background-position: top center;
background-color: transparent
}