app/views/devise/sessions/new.html.erb
<%= simple_form_for(resource, as: resource_name, url: session_path(resource_name), :class => 'simple_form') do |f| %>
<div class="login_input">
<div class="input-prepend">
<span class="add-on"><img src="/assets/man.png" /></span>
<%= f.text_field :id_connexion, required: false, autofocus: true, :label => I18n.t('login_name'), :class => 'login_username', :placeholder => I18n.t('login_name_or_email') %>
</div>
<div class="input-prepend">
<span class="add-on"><img src="/assets/keez.png" /></span>
<%= f.password_field :password, required: false, :label => I18n.t('password'), :class => 'login_pw', :placeholder => I18n.t('password')%>
</div>
<label class="checkbox">
<%= f.check_box :remember_me, :label => I18n.t(:remember_me), as: :boolean if devise_mapping.rememberable? %>
<%= I18n.t(:remember_me ) %>
</label>
</div>
<div>
<%= f.button :submit, I18n.t('connect'), :class => "btn btn-danger" %>
</div>
<% end %>
<%= render "devise/shared/links" %>