# Customizing Your Theme

Altering a theme to suit your needs.

---

If you would like to make a few tweaks to an existing theme, there is no need
to create your own theme from scratch. For minor tweaks which only require
some CSS and/or JavaScript, you can [use the docs_dir](#using-the-docs_dir).
However, for more complex customizations, including overriding templates, you
will need to [use the theme custom_dir](#using-the-theme-custom_dir) setting.

## Using the docs_dir

The [extra_css] and [extra_javascript] configuration options can be used to
make tweaks and customizations to existing themes. To use these, you simply
need to include either CSS or JavaScript files within your [documentation
directory].

For example, to change the color of the headers in your documentation, create
a file called (for example) `style.css` and place it next to the documentation Markdown. In
that file add the following CSS.

```css
h1 {
  color: red;
}
```

Then you need to add it to `mkdocs.yml`:

```yaml
extra_css:
  - style.css
```

After making these changes, they should be visible when you run
`mkdocs serve` - if you already had this running, you should see that the CSS
changes were automatically picked up and the documentation will be updated.

NOTE:
Any extra CSS or JavaScript files will be added to the generated HTML
document after the page content. If you desire to include a JavaScript
library, you may have better success including the library by using the
theme [custom_dir].

## Using the theme custom_dir

The [`theme.custom_dir`][custom_dir] configuration option can be used to point
to a directory of files which override the files in a parent theme. The parent
theme would be the theme defined in the [`theme.name`][name] configuration
option. Any file in the `custom_dir` with the same name as a file in the
parent theme will replace the file of the same name in the parent theme. Any
additional files in the `custom_dir` will be added to the parent theme. The
contents of the `custom_dir` should mirror the directory structure of the
parent theme. You may include templates, JavaScript files, CSS files, images,
fonts, or any other media included in a theme.

NOTE:
For this to work, the `theme.name` setting must be set to a known
installed theme. If the `name` setting is instead set to `null` (or not
defined), then there is no theme to override and the contents of the
`custom_dir` must be a complete, standalone theme. See the [Theme
Developer Guide][custom theme] for more information.

For example, the [mkdocs] theme ([browse source]), contains the following
directory structure (in part):

```text
- css\
- fonts\
- img\
  - favicon.ico
  - grid.png
- js\
- 404.html
- base.html
- content.html
- nav-sub.html
- nav.html
- toc.html
```

To override any of the files contained in that theme, create a new directory
next to your `docs_dir`:

```bash
mkdir custom_theme
```

And then point your `mkdocs.yml` configuration file at the new directory:

```yaml
theme:
  name: mkdocs
  custom_dir: custom_theme/
```

To override the 404 error page ("file not found"), add a new template file named
`404.html` to the `custom_theme` directory. For information on what can be
included in a template, review the [Theme Developer Guide][custom theme].

To override the favicon, you can add a new icon file at
`custom_theme/img/favicon.ico`.

To include a JavaScript library, copy the library to the `custom_theme/js/`
directory.

Your directory structure should now look like this:

```text
- docs/
  - index.html
- custom_theme/
  - img/
    - favicon.ico
  - js/
    - somelib.js
  - 404.html
- config.yml
```

NOTE:
Any files included in the parent theme (defined in `name`) but not
included in the `custom_dir` will still be utilized. The `custom_dir` will
only override/replace files in the parent theme. If you want to remove
files, or build a theme from scratch, then you should review the [Theme
Developer Guide][custom theme].

### Overriding Template Blocks

The built-in themes implement many of their parts inside template blocks which
can be individually overridden in the `main.html` template. Simply create a
`main.html` template file in your `custom_dir` and define replacement blocks
within that file. Just make sure that the `main.html` extends `base.html`. For
example, to alter the title of the MkDocs theme, your replacement `main.html`
template would contain the following:

```django
{% extends "base.html" %}

{% block htmltitle %}
<title>Custom title goes here</title>
{% endblock %}
```

In the above example, the `htmltitle` block defined in your custom `main.html` file
will be used in place of the default `htmltitle` block defined in the parent theme.
You may re-define as many blocks as you desire, as long as those blocks are
defined in the parent. For example, you could replace the Google Analytics
script with one for a different service or replace the search feature with your
own. You will need to consult the parent theme you are using to determine what
blocks are available to override. The MkDocs and ReadTheDocs themes provide the
following blocks:

* `site_meta`: Contains meta tags in the document head.
* `htmltitle`: Contains the page title in the document head.
* `styles`: Contains the link tags for stylesheets.
* `libs`: Contains the JavaScript libraries (jQuery, etc) included in the page header.
* `scripts`: Contains JavaScript scripts which should execute after a page loads.
* `analytics`: Contains the analytics script.
* `extrahead`: An empty block in the `<head>` to insert custom tags/scripts/etc.
* `site_name`: Contains the site name in the navigation bar.
* `site_nav`: Contains the site navigation in the navigation bar.
* `search_button`: Contains the search box in the navigation bar.
* `next_prev`: Contains the next and previous buttons in the navigation bar.
* `repo`: Contains the repository link in the navigation bar.
* `content`: Contains the page content and table of contents for the page.
* `footer`: Contains the page footer.

You may need to view the source template files to ensure your modifications will
work with the structure of the site. See [Template Variables] for a list of
variables you can use within your custom blocks. For a more complete
explanation of blocks, consult the [Jinja documentation].

### Combining the custom_dir and Template Blocks

Adding a JavaScript library to the `custom_dir` will make it available, but
won't include it in the pages generated by MkDocs. Therefore, a link needs to
be added to the library from the HTML.

Starting the with directory structure above (truncated):

```text
- docs/
- custom_theme/
  - js/
    - somelib.js
- config.yml
```

A link to the `custom_theme/js/somelib.js` file needs to be added to the
template. As `somelib.js` is a JavaScript library, it would logically go in the
`libs` block. However, a new `libs` block that only includes the new script will
replace the block defined in the parent template and any links to libraries in
the parent template will be removed. To avoid breaking the template, a
[super block] can be used with a call to `super` from within the block:

```django
{% extends "base.html" %}

{% block libs %}
    {{ super() }}
    <script src="{{ base_url }}/js/somelib.js"></script>
{% endblock %}
```

Note that the [base_url] template variable was used to ensure that the link is
always relative to the current page.

Now the generated pages will include links to the template provided libraries as
well as the library included in the `custom_dir`. The same would be required for
any additional CSS files included in the `custom_dir`.

[custom theme]: ../dev-guide/themes.md
[extra_css]: ./configuration.md#extra_css
[extra_javascript]: ./configuration.md#extra_javascript
[documentation directory]: ./configuration.md#docs_dir
[custom_dir]: ./configuration.md#custom_dir
[name]: ./configuration.md#name
[mkdocs]: ./choosing-your-theme.md#mkdocs
[browse source]: https://github.com/mkdocs/mkdocs/tree/master/mkdocs/themes/mkdocs
[Template Variables]: ../dev-guide/themes.md#template-variables
[Jinja documentation]: https://jinja.palletsprojects.com/en/latest/templates/#template-inheritance
[super block]: https://jinja.palletsprojects.com/en/latest/templates/#super-blocks
[base_url]: ../dev-guide/themes.md#base_url