style support request form

Summary:
Styles the create support request form similarly to the details form, using the standard UI components.

N.B. Video section styling will be a separate diff

Reviewed By: jknoxville

Differential Revision: D18637989

fbshipit-source-id: f1cc6967b6841a55e770043f330e1a87ac7bfb50

src/ui/components/HBox.tsx

@@ -42,7 +42,9 @@ const HBox: React.FC<{
     width: '100%',
     shrink: 1,
     grow: 1,
-  };
+    display: 'flex',
+    flexDirection: 'column',
+  } as const;
 
   switch (grow) {
     case 'right':