Adding a login form in the submenu

Hi Enfold team

I want to add a customized login form to the submenu part instead of using existing page links. I have two question to achieve this:

1.Which template file should be modify for this behavior? and which action hook should I use to add this function?

2.Do you have existing login form template file or function that I can use for this behavior? And which css definition should I look into if I want to change the styling?

BR//

Heng GAO