You should edit the CSS style file: /usr/local/elog/themes/default/elog.css

This has nothing to do with the ELOG package, but only with your local configuration of that specific logbook.
You should contact your local ELOG administrator.

Or you might want to rephrase you question: do you want to have this text added in the text field when selecting the field specifier?
How that can be done depends on your specific configuration. Since you are apparently already using a form in the text field, it might be tricky.

Yes, you can see that in the logging file, if you turn on logging. You might want to read the manual https://elog.psi.ch/elog/config.html. Here's the relevant excerpt:

• Logfile = <file>
  This option specifies a filename which logs all login/logout activities and successful user connections for logbooks with user level access. The the logging level (see below) is larger than 1, also read and write accesses can be logged.
• Logging level = 1 | 2 | 3
  Specifies the logging level. The higher this value, the more information is logged. Default is 2:
  • 1: Log only logins and logouts
  • 2: Log also write accesses
  • 3: Log also read accesses