Design
The login page in Shesha is a configurable form, not hard-coded markup. It is a configuration item identified as Shesha/login (Shesha is the module, login is the form name), so you can open it in the form designer and change it like any other form.
Because it ships as a standard Shesha form, the default login page can log a user in out of the box, but you can also customize what happens before and after the login process, for example running a script when login fails or redirecting to a different page on success.
If you are upgrading an older Shesha application that predates the configurable login page, you need to run the latest database migrations before the Shesha/login form configuration becomes available to edit.
Look and Feel
Out of the box, the configurable login page looks identical to the classic, hard-coded login page it replaced. Since it is now a regular form, you can redesign it completely using the same form components and settings you would use on any other Shesha form.
To open the Shesha/login form for editing, find it in Configuration Studio's Solution Explorer and use the designer to change its layout. See Editing items for how configuration items like forms are opened and edited.