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. However, for more complex customizations, including overriding templates, you will need to use 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 extra.css and place it next to the documentation Markdown. In that file add the following CSS.

h1 {
  color: red;


If you are deploying your documentation with ReadTheDocs. You will need to explicitly list the CSS and JavaScript files you want to include in your config. To do this, add the following to your mkdocs.yml.

extra_css: [extra.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.


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 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 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.


For this to work, the 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 for more information.

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

- 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:

mkdir custom_theme

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

    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.

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:

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


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.

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:

{% 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):

- 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:

{% 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.