Fix isInternalUrl for subdomain support

Refactor / reduce plumbing

app/components/CenteredContent.js

@@ -0,0 +1,32 @@
+// @flow
+import * as React from 'react';
+import styled from 'styled-components';
+import breakpoint from 'styled-components-breakpoint';
+
+type Props = {
+  children?: React.Node,
+};
+
+const Container = styled.div`
+  width: 100%;
+  padding: 60px 20px;
+
+  ${breakpoint('tablet')`
+    padding: 60px;
+  `};
+`;
+
+const Content = styled.div`
+  max-width: 46em;
+  margin: 0 auto;
+`;
+
+const CenteredContent = ({ children, ...rest }: Props) => {
+  return (
+    <Container {...rest}>
+      <Content>{children}</Content>
+    </Container>
+  );
+};
+
+export default CenteredContent;