<%= form_for @post do |f| %>
  <div class="form-group">
    <%= f.text_field :title, class: 'form-control', placeholder: 'Title' %>
  </div>

  <div class="form-group">
    <%= f.text_area :body, class: 'form-control',
      placeholder: 'Write your story here ...', rows: 30 %>
  </div>

  <div class="form-group">
    <%= f.text_field :all_tags, class: 'form-control', placeholder: 'Tags separated by a comma ...' %>
  </div>

  <%= f.submit "Publish", class: "btn btn-primary" %>
<% end %>

<%= form_for @post do |f| %>
  <div class="form-group">
    <%= f.text_field :title, class: 'form-control', placeholder: 'Title' %>
  </div>

  <div class="form-group">
    <%= f.text_area :body, class: 'form-control',
      placeholder: 'Write your story here ...', rows: 30 %>
  </div>

  <div class="form-group">
    <%= f.text_field :all_tags, class: 'form-control', placeholder: 'Tags separated by a comma ...' %>
  </div>

  <%= f.submit "Publish", class: "button green-inner-button" %>
<% end %>

Update CSS styles for publish button
Update CSS styles for publish button
