[feature] Add theme selector to app settings

app/javascript/flavours/glitch/containers/theme_component.jsx

@@ -0,0 +1,36 @@
+import PropTypes from 'prop-types';
+import React from 'react';
+
+import { useAppSelector } from 'flavours/glitch/store';
+
+const ThemeComponent = ({ children }) => {
+  const theme = useAppSelector(
+    (state) => state.getIn(['local_settings', 'theme']) ?? 'mastodon-light',
+  );
+
+  let href;
+  switch (true) {
+  case theme === 'mastodon':
+    href = '';
+    break;
+  case theme === 'mastodon-light':
+    href = '/packs/css/skins/glitch/mastodon-light/common.css';
+    break;
+  case theme === 'contrast':
+    href = '/packs/css/skins/glitch/contrast/common.css';
+    break;
+  }
+
+  return (
+    <>
+      {href !== '' ? <link rel='stylesheet' media='all' href={href} /> : null}
+      {children}
+    </>
+  );
+};
+
+ThemeComponent.propTypes = {
+  children: PropTypes.node,
+};
+
+export { ThemeComponent };