How to customize the login form with css, outerclasses and classes

Hi,

How can I customize the login form template with custom css and outerclasses and classes in md files?

Now I have my login form like this:

I want to center all elements, but I’ve couldn’t still. I’ve changed the login.css and I’ve tried to set some outerclasses and classes (col-md-6 and col-md-12 and classes: form-control input-lg) in login.md, but I have not got what I want.

In login.css I’ve modified the text-align property and work for labels, but not for input boxes

#grav-login {
    max-width: 70rem;
    margin: 5rem auto;
    background: #fcfcfc;
    border: 4px solid #eee;
    border-radius: 4px;
    padding: 1rem 3rem 3rem 3rem;
    text-align: center;
}

Have you got any idea about how I can to customize this login form?

Thanks very much.