How to create a custom theme for Horizon

Based on the idea or proposal of Kieran Spear, I'll document here, what has to be done, if one needs to customize Horizon (for whatever reason).

Let's say, one needs to create a corporate theme, named horizon_bigcorp. Then we first need to change local_settings.py. In Fedora and EPEL, that file is located at /etc/openstack-dashboard/local_settings

Append the following lines to that file

THEME_APP = 'horizon_bigcorp'

try:
    __import__(THEME_APP)
    INSTALLED_APPS = (THEME_APP,) + INSTALLED_APPS
except:
    pass
Then we'll create a customization app:
├── __init__.py
├── __init__.pyc
├── models.py
├── models.pyc
├── static
│   └── dashboard
│       ├── img
│       │   ├── bigcorpfavicon.ico
│       │   └── bigcorplogo.png
│       └── less
│           └── bigcorptheme.less
└── templates
    ├── horizon
    │   └── common
    │       └── _sidebar.html
    └── _stylesheets.html

7 directories, 9 files
Those .py files just need to be empty files.
The magic is in _stylesheets.html, it's basically a modified copy

System Message: WARNING/2 (/home/mrunge/work/blog/content/2013/how-to-create-a-custom-theme-for-horizon.rst, line 53)

Line block ends without a blank line.

of file openstack_dashboard/templates/_stylesheets.html:

{% load compress %}

{% compress css %}
<link href='{{ STATIC_URL }}dashboard/less/horizon.less' type='text/less' media='screen' rel='stylesheet' />
{% endcompress %}

<link rel="shortcut icon" href="{{ STATIC_URL }}dashboard/img/favicon.ico"/>

Note, you just need a customized theme.less, if you did changes at css (most likely). Like stylesheets, theme.less is a modified copy of it's counterpart taken from the openstack_dashboard directory.

Another example, how this can be implemented can be found here: https://github.com/mrunge/horizon/tree/customization, where I modified settings.py instead of changing local_settings.py.example