# Theming

Since version 3.0.0, GitBook can be easily themed. Books use the [theme-default](https://github.com/GitbookIO/theme-default) theme by default.

> **Caution**: Custom theming can block some plugins from working correctly.

### Structure of a theme

A theme is a plugin containing templates and assets. Overriding any individual template is optional, since themes always extend the default theme.

| Folder | Description |
| -------- | ----------- |
| `_layouts` | Main folder containing all the templates |
| `_layouts/website/page.html` | Template for a normal page |
| `_layouts/ebook/page.html` | Template for a normal page during ebook generation (PDF< ePub, Mobi) |


### Extend/Customize theme in a book

Authors can extend the templates of a theme directly from their book's source (without creating an external theme). Templates will be resolved in the `_layouts` folder of the book first, then in the installed plugins/themes.

### Extend instead of Forking

When you want to make your theme changes available to multiple books, instead of forking the default theme, you can extend it using the [templating syntax](../templating/README.md):

```html
{% extends template.self %}

{% block body %}
    {{ super() }}
    ... This will be added to the "body" block
{% endblock %}
```

Take a look at the [API](https://github.com/GitbookIO/theme-api) theme for a more complete example.

### Publish a theme

Themes are published as plugins ([see related docs](../plugins/README.md)) with a `theme-` prefix. For example the theme `awesome` will be loaded from the `theme-awesome` plugin, and then from the `gitbook-plugin-theme-awesome` NPM package.