Bootstrap login button not the color I'm expecting

In my app/views/users/sessions/new.html.slim, I have:

.container
  = form_for(resource, as: resource_name, url: session_path(resource_name), html: {class: "form-signin"}) do |f|
    h2.form-signin-heading
      = t('users.mailer.registrations.sessions.new.please_sign_in')
    .form-group
      .sr-only
        = f.label t('users.sessions.new.email_address')
      = f.email_field :email, class: 'form-control form-signin email_input', autofocus: true, placeholder: "Email Address", required: ""
      .sr-only
        = f.label t('users.sessions.new.password')
      = f.password_field :password, class: 'form-control form-signin password_input', autofocus: true, placeholder: "Password", required: ""
    - if devise_mapping.rememberable?
      .checkbox
        label
          = f.check_box :remember_me
          = t('users.sessions.new.remember_me')
    .form-group
      = f.submit t('users.mailer.sessions.new.log_in'), class: "form-control button.btn.btn-lg.btn-primary.btn-block"
    .form-group
      .col-md-offset-4.col-md-8
       = render "devise/shared/links"

In my assets/stylesheets/signin.css.scss, (I import it into applicatio.css.scss), I have:

.form-signin {
  max-width: 330px;
  padding: 15px;
  margin: 0 auto;
}
.form-signin body {
  padding-top: 40px;
  padding-bottom: 40px;
  background-color: #ee
}
.form-signin .form-signin-heading,
.form-signin .checkbox {
  text-align: center;
  margin-bottom: 10px;
}
.form-signin .checkbox {
  font-weight: normal;
}
.form-signin .form-control {
  position: relative;
  height: auto;
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
  padding: 10px;
  font-size: 16px;
}
.form-signin .form-control:focus {
  z-index: 2;
}
.form-signin .email_input {
  margin-bottom: -1px;
  border-bottom-right-radius: 0;
  border-bottom-left-radius: 0;
}
.form-signin .password_input {
  margin-bottom: 10px;
  border-top-left-radius: 0;
  border-top-right-radius: 0;
}      

I am expecting the login button to be blue, but it's white. Any idea what I'm doing incorrectly?

Wrong class on submit form helper, you should make it like this: f.submit t('users.mailer.sessions.new.log_in'), class: "form-control btn btn-lg btn-primary btn-block" Divide classes with spaces.