The CSS web file is provided

mfoss — Mon, 25 Nov 2013 10:46:34 +0000

The CSS web file is provided directly by mod_register_web erlang code. So, to modify the content of the CSS web file:
1. Edit mod_register_web.erl
2. Modify the lines that say:

css() -> 
    "html,body {
background: white;
margin: 0;
padding: 0;
height: 100%;
}".

3. Compile that file with an Erlang version similar to the one you are using to run ejabberd:
erlc mod_register_web.erl
4. Copy the binary file mod_register_web.beam to overwrite the old one (keep a backup in case it has some bug).
5. Restart ejabberd.

ejabberd - Comments for "CSS for Registration Page"

The CSS web file is provided