Expand uploaded thumbnail (#2611)

app/assets/javascripts/components/features/compose/components/upload_form.jsx

@@ -18,7 +18,7 @@ class UploadForm extends React.PureComponent {
       <div className='compose-form__upload' key={attachment.get('id')}>
         <Motion defaultStyle={{ scale: 0.8 }} style={{ scale: spring(1, { stiffness: 180, damping: 12 }) }}>
           {({ scale }) =>
-            <div className='compose-form__upload-thumbnail' style={{ transform: `translateZ(0) scale(${scale})`, background: `url(${attachment.get('preview_url')}) no-repeat center` }}>
+            <div className='compose-form__upload-thumbnail' style={{ transform: `translateZ(0) scale(${scale})`, backgroundImage: `url(${attachment.get('preview_url')})` }}>
               <IconButton icon='times' title={intl.formatMessage(messages.undo)} size={36} onClick={this.props.onRemoveFile.bind(this, attachment.get('id'))} />
             </div>
           }

app/assets/stylesheets/components.scss

@@ -274,6 +274,9 @@
 
 .compose-form__upload-thumbnail {
   border-radius: 4px;
+  background-position: center;
+  background-size: cover;
+  background-repeat: no-repeat;
   height: 100px;
   width: 100%;
 }