Hi, welcome 
You can add CSS in your themes or a separate theme component:
For example, assuming you want to add an image to the category ID 4, you would do something like that:
.category-list .category-list-banner {
&.category-4 {
background-image: url(https://images.unsplash.com/32/Mc8kW4x9Q3aRR3RkP5Im_IMG_4417.jpg);
background-size: cover;
}
}
This is just an example. For more information, you can look at the background
CSS properties.
Also helpful links
:
2 Likes