cherry-pick conflicts.

stylesheets/_session_theme.scss

@@ -49,8 +49,14 @@
   }
 
   &__container--outgoing {
-    @include themify($themes) {
+    &--opaque {
-      background: themed('sentMessageBackground');
+      @include themify($themes) {
+        background: themed('sentMessageBackground');
+      }
+    }
+
+    &--transparent {
+      background: none;
     }
 
     .module-message__text {

ts/components/conversation/Message.tsx

@@ -781,7 +781,10 @@ class MessageInner extends React.PureComponent<MessageRegularProps, State> {
           <div
             className={classNames(
               'module-message__container',
-              `module-message__container--${direction}`
+              `module-message__container--${direction}`,
+              isShowingImage
+                ? `module-message__container--${direction}--transparent`
+                : `module-message__container--${direction}--opaque`
             )}
             style={{
               width: isShowingImage ? width : undefined,