Responsive CSS updates.

components/layout/PageHeader.js

@@ -1,6 +1,7 @@
 import React from 'react';
+import classNames from 'classnames';
 import styles from './PageHeader.module.css';
 
-export default function PageHeader({ children }) {
-  return <div className={styles.header}>{children}</div>;
+export default function PageHeader({ children, className }) {
+  return <div className={classNames(styles.header, className)}>{children}</div>;
 }