Fix background-size being overwritten (#2382)

app/assets/javascripts/components/components/media_gallery.jsx

@@ -86,7 +86,7 @@ class Item extends React.PureComponent {
           href={attachment.get('remote_url') || attachment.get('url')}
           onClick={this.handleClick}
           target='_blank'
-          style={{ background: `url(${attachment.get('preview_url')}) no-repeat center`}}
+          style={{ backgroundImage: `url(${attachment.get('preview_url')})` }}
         />
       );
     } else if (attachment.get('type') === 'gifv') {

app/assets/stylesheets/components.scss

@@ -2999,6 +2999,8 @@ button.icon-button.active i.fa-retweet {
 }
 
 .media-gallery__item-thumbnail {
+  background-position: center;
+  background-repeat: no-repeat;
   background-size: cover;
   cursor: zoom-in;
   display: block;