Moved code into src folder. Added build for component library.

src/pages/404.js

@@ -0,0 +1,19 @@
+import { Row, Column, Flexbox } from 'react-basics';
+import AppLayout from 'components/layout/AppLayout';
+import useMessages from 'components/hooks/useMessages';
+
+export default function Custom404() {
+  const { formatMessage, labels } = useMessages();
+
+  return (
+    <AppLayout title={formatMessage(labels.pageNotFound)}>
+      <Row>
+        <Column>
+          <Flexbox alignItems="center" justifyContent="center" flex={1} style={{ minHeight: 600 }}>
+            <h1>{formatMessage(labels.pageNotFound)}</h1>
+          </Flexbox>
+        </Column>
+      </Row>
+    </AppLayout>
+  );
+}