refactor(v2): split out dark mode toggle so it is easily swizzle-able (#2013)

packages/docusaurus-theme-classic/src/theme/Toggle/index.js

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import React from 'react';
+import Toggle from 'react-toggle';
+
+import classnames from 'classnames';
+import styles from './styles.module.css';
+
+const Moon = () => <span className={classnames(styles.toggle, styles.moon)} />;
+const Sun = () => <span className={classnames(styles.toggle, styles.sun)} />;
+
+export default function(props) {
+  return (
+    <Toggle
+      icons={{
+        checked: <Moon />,
+        unchecked: <Sun />,
+      }}
+      {...props}
+    />
+  );
+}