chrone: sperate client and server to different repos.

src/components/Postbox.js

@@ -0,0 +1,41 @@
+import React, { useState } from 'react';
+import { Collapse } from '@blueprintjs/core';
+import classNames from 'classnames';
+
+/**
+ * Postbox.
+ */
+export default function Postbox({
+  defaultOpen = true,
+  toggable = true,
+  title,
+  children,
+}) {
+  const [isOpen, setIsOpen] = useState(defaultOpen);
+
+  // Handle the title click.
+  const handleTitleClick = () => {
+    if (toggable) {
+      setIsOpen(!isOpen);
+    }
+  };
+
+  return (
+    <div
+      class={classNames('postbox', {
+        'is-toggable': toggable,
+      })}
+    >
+      <div class="postbox__header" onClick={handleTitleClick}>
+        <h5 class="postbox__title">{title}</h5>
+
+        <span class="postbox__toggle-indicator"></span>
+      </div>
+      <div class="postbox__content">
+        <Collapse isOpen={isOpen}>
+          <div class="postbox__content-inner">{children}</div>
+        </Collapse>
+      </div>
+    </div>
+  );
+}