_form.html.erb

<%= form_with(model: @activity) do |form| %>
  <% if @activity.errors.any? %>
    <div style="color: red">
      <h2><%= pluralize(@activity.errors.count, "error") %> prohibited this activity from being saved:</h2>

      <ul>
        <%= @activity.errors.each do |error| %>
          <li><%= error.full_message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <div>
    <%= form.label :title, style: "display: block" %>
    <%= form.text_field :title %>
  </div>

  <div>
    <%= form.label :activity_type, style: "display: block" %>
    <%= form.text_field :activity_type %>
  </div>

  <div>
    <%= form.label :start, style: "display: block" %>
    <%= form.datetime_field :start %>
  </div>

  <div>
    <%= form.label :duration, style: "display: block" %>
    <%= form.text_field :duration %>
  </div>

  <div>
    <%= form.label :calories, style: "display: block" %>
    <%= form.number_field :calories %>
  </div>

  <div>
    <%= form.submit %>
  </div>
<% end %>