List templates

docker exec -it horizon bash
ls -l /var/lib/kolla/venv/lib/python2.7/site-packages/openstack_dashboard/themes

Configure theme
/etc/kolla/horizon/custom_local_settings

AVAILABLE_THEMES = [
    ('default', 'Default', 'themes/default'),
    ('foo_bar', 'Foo bar', 'themes/foo_bar')
]

SELECTABLE_THEMES = [
    ('foo_bar', 'Foo bar', 'themes/foo_bar')
]

DEFAULT_THEME = 'foo_bar'