...

# tree /var/www/html/ui/
/var/www/html/ui
|-- config
|   |-- theme1.json
|   |-- theme2.json
...
|-- theme
|   |-- abicloudDefault
...
|-- theme1
...
|-- theme2
...

To avoid login errors, you must configure the default theme. For example, you can create a theme folder called empty, and add an empty theme.css file, and then in the theme folder, set empty as the default theme. 

> theme/ ln -s empty default

For more details, see https://abiquo.atlassian.net/wiki/spaces/doc/pages/311374572/Abiquo+branding+guide#Set-a-default-theme-for-login-and-enterprises-without-themes

You can have different property configurations in each config json file, but it is very important that the config.endpoint property points to its related API subdomain URL:

# grep endpoint /var/www/html/ui/config/*
/var/www/html/ui/config/theme1.json: "config.endpoint": "https://theme1.example.com/api",
/var/www/html/ui/config/theme2.json: "config.endpoint": "https://theme2.example.com/api",

Now place your customized themes in the Abiquo UI root folder with a suitable name and ensure that the structure is as described above.

When users load the UI, to prevent a 404 error in the browser console because the default theme.css is not found, set a default theme, which can be the empty theme.
See Abiquo+branding+guide#Set-a-default-theme-for-login-and-enterprises-without-themes.

Apache SSL front-end

Apache will provide the SSL layer to Abiquo components and serve the Abiquo UI. We need to tell Apache to work with NameVirtualHost directive because we want to serve different content depending on the accessed hostname.
Ensure that NameVirtualHost directive is enabled for both HTTP and HTTPS protocols:

...