app/views/admin/sessions/new.html.erb
<div class="row">
<%= form_for resource, as: resource_name, url: session_path(resource_name),
html: { class: 'col-md-6 form-signin center-block text-center' } do |f| %>
<h1 class="form-signin-heading text-center"><%= t '.header_html' %></h1>
<hr>
<%= f.label :username, class: 'sr-only' %>
<%= f.text_field :username, placeholder: AdminUser.human_attribute_name(:username),
required: true,
autofocus: true,
class: 'form-control' %>
<%= f.label :password, class: 'sr-only' %>
<%= f.password_field :password, placeholder: AdminUser.human_attribute_name(:password),
required: true,
class: 'form-control' %>
<%= f.submit t('.sign_in_btn'), class: 'btn btn-lg btn-primary btn-block' %>
<% end %>
</div>
<%= render 'links' %>