How can I make a collection image full width on studio theme?

Hi I have an image thats within the collection description on studio theme. At the moment it is sitting to the left and i would like it as a full width banner. When i edit the image to a 600px banner it still remains the same side and to the left of the screen. Does anyone have a fix?

Many thanks

Add this code in css file

.collection-description img {
  width: 100%;
  height: auto;
  display: block;
  margin: 0 auto;
}

Hi - this has not worked. Im adding to templates-collections.css?

@Tucks1985

Please share your store URL!

Thanks!

H, here’s a link to the preview

https://xrgeo1h8izxkodfq-74844307762.shopifypreview.com