= semantic_form_for @activity do |f|
  = f.inputs do
    = f.input :project, :as => :combobox
    = f.input :person, :as => :combobox
  = f.inputs do
    = f.input :date, :as => :date_field, :required => true
    = f.input :duration_from, :as => :hour_field
    = f.input :duration_to, :as => :hour_field
    = f.input :hours
    = f.input :minutes
  = f.inputs do
    = f.input :comment
  = f.buttons do
    = f.commit_button

= semantic_form_for @activity do |f|
  = f.inputs do
    = f.input :project, :as => :combobox
    = f.input :person, :as => :combobox

  = f.inputs do
    = f.input :date, :as => :date_field, :required => true
    = f.input :duration_from, :as => :hour_field
    = f.input :duration_to, :as => :hour_field
    = f.input :hours
    = f.input :minutes

  = f.inputs do
    = f.input :comment

  = f.buttons do
    = f.commit_button

Add some empty lines to activities/form.
Add some empty lines to activities/form.
