Use JS to customize the login page


I wanted to inquire if it is possible to customize the login page using JavaScript. The goal is to modify the behavior of the alert on the login page, such as changing the green notify bubble to red when there are warning messages. The basic code has already been written; the question is whether it is possible to insert this code directly into the ServiceDesk, or if there is a JavaScript file where the code can be added.

Thank you.