App configs are where you can define the global settings of the site. App configs define fundamental settings that are not only limited to the theme configs such as configuration for "base directory", or the "title" of the site.
```ts
export default {
// These are app level configs.
lang: 'en-US',
title: 'VitePress',
description: 'Vite & Vue powered static site generator.',
Whether to enable "Dark Mode" or not. If the option is set to `true`, it adds `.dark` class to the `<html>` tag depending on the users preference.
It also injects inline script that tries to read users settings from local storage by `vitepress-theme-appearance` key and restores users preferred color mode.
The base URL the site will be deployed at. You will need to set this if you plan to deploy your site under a sub path, for example, GitHub pages. If you plan to deploy your site to `https://foo.github.io/bar/`, then you should set base to `'/bar/'`. It should always start and end with a slash.
The base is automatically prepended to all the URLs that start with / in other options, so you only need to specify it once.
Additional elements to render in the `<head>` tag in the page HTML. The user-added tags are rendered before the closing `head` tag, after VitePress tags.
Use git commit to get the timestamp. This option enables the default theme to display the page's last updated time. You can customize the text via [`themeConfig.lastUpdatedText`](theme-configs#lastupdatedtext) option.
Configure Markdown parser options. VitePress uses [Markdown-it](https://github.com/markdown-it/markdown-it) as the parser, and [Shiki](https://shiki.matsu.io/) to highlight language syntax. Inside this option, you may pass various Markdown related options to fit your needs.
The suffix for the title. For example, if you set `title` as `VitePress` and set `titleTemplate` as `My Site`, the html title becomes `VitePress | My Site`.
Set `false` to disable the feature. If the option is `undefined`, then the value of `title` option will be used.
Enabling this may require additional configuration on your hosting platform. For it to work, your server must serve the generated page on requesting the URL (see above table) **without a redirect**.
`transformHead` is a build hook to transform the head before generating each page. It will allow you to add head entries that cannot be statically added to your VitePress config. You only need to return extra entries, they will be merged automatically with the existing ones.
