<div class="login form-container col-md-4">

  <h3>Login</h3>

  <%= render 'sessions/errors' if @errors %>

  <%= form_tag(sessions_path, method: 'post', id: 'login-form') do %>
    <div class="input-container username">
      <%= label_tag :username, nil, :class => 'session-label' %>
      <%= text_field_tag :username, 'Username', :class => 'form-control' %>
    </div>
    <div class="input-container password">
      <%= label_tag :password, nil, :class => 'session-label' %>
      <%= password_field_tag :password, nil, :class => 'form-control' %>
    </div>
    <input type='submit' class='btn btn-primary' value='Login'>
    <%= link_to "Need to register?", new_user_path %>
  <% end %>
</div>

<div class="login form-container col-md-4">

  <h3>Login</h3>

  <%= render 'sessions/errors' if @errors %>

  <%= form_tag(sessions_path, method: 'post', id: 'login-form') do %>
    <div class="input-container username">
      <%= label_tag :username, nil, :class => 'session-label' %>
      <%= text_field_tag :username, nil, placeholder: "Username", :class => 'form-control' %>
    </div>
    <div class="input-container password">
      <%= label_tag :password, nil, :class => 'session-label' %>
      <%= password_field_tag :password, nil, :class => 'form-control' %>
    </div>
    <input type='submit' class='btn btn-primary' value='Login'>
    <%= link_to "Need to register?", new_user_path %>
  <% end %>
</div>

Fix placeholder on login form
Fix placeholder on login form
