At the beginning of simplicit development, I used built-in sign in form from devise plugin. And honestly, the layout is very bad. I find a way to modify the built-in form, but I thought that wasn’t wise. How should I modify the layout when I need to deploy it? So troublesome!
That’s why, I just found out how to make a custom sign in form. Thanks to devise complete documentation at https://github.com/plataformatec/devise/wiki/_pages. You won’t find a boring sign in form anymore in simplicit. It has been combined with admin layout page. I can change the layout anytime and any kind I want. This is the screen shoot of the sign in page of simplicit. The layout is still so simple, but for next development I’ll make it more beautiful.