Clean up css and remove keydown suppression

src/outputarea/index.css

@@ -101,6 +101,11 @@
 }
 
 
+.jp-OutputAreaWidget-output {
+  display: flex;
+}
+
+
 /* Hide the gutter in case of
  *  - nested output areas (e.g. in the case of output widgets)
  *  - mirrored output areas

src/outputarea/widget.ts

@@ -596,8 +596,6 @@ namespace OutputAreaWidget {
           }
           this.node.replaceChild(rendered, input);
         }
-        // Suppress keydown events from leaving the input.
-        event.stopPropagation();
       }
     }