Load favicon from CSS dir
The favicon.ico should be CSS-dependent to ease the change.
Technically, this just means changing the favicon.ico tag at the beginning of the HTML page:
<link rel="shortcut icon" href="https://my.chamilo.net/favicon.ico" type="image/x-icon" />
to something like
<link rel="shortcut icon" href="https://my.chamilo.net/main/css/chamilo/images/favicon.ico" type="image/x-icon" />
(after checking that this file exists, of course, otherwise we should stick to the base style).
The only possible discussion about this is whether it should rather depend of the multi-url directory instead of the CSS, but given you can change the CSS by multi-URL, there's no real need to consider it.