Container: support flexbox directives.

src/widgets/Container.tsx

@@ -6,12 +6,17 @@ import Paper from "@material-ui/core/Paper";
 
 import "./Container.css";
 
-export default (props: {style?: any, children: any}) => (
+export default (props: {style?: React.CSSProperties, children: any}) => {
+  const display = props.style?.display;
+  const flexDirection = props.style?.flexDirection;
+
+  return (
     <div className="Container" style={props.style}>
-    <Paper elevation={3}>
-      <div className="Container-inner">
+      <Paper elevation={3} style={{ display, flexDirection, flexGrow: 1 }}>
+        <div className="Container-inner" style={{ display, flexDirection, flexGrow: 1 }}>
           {props.children}
         </div>
       </Paper>
     </div>
-);
+  );
+};