discourse/app/views/user_notifications/digest.html.erb

<table style="border: 1px solid #ddd;" cellspacing="0" cellpadding="0">
<tr>
  <td style="padding: 10px 10px; background-color: #eee; border: 1px solid #ddd;">
    <a href="<%= Discourse.base_url %>">
    <img src="<%= logo_url %>" style="max-height: 35px; min-height: 35px; height: 35px;" class='site-logo'></a>
  </td>
</tr>
<tr>
  <td style="background-color: #fff; padding: 10px 10px; font-family: Arial, Helvetica, sans-serif; font-size: 14px;">
    <%= raw(t 'user_notifications.digest.why', site_link: html_site_link, last_seen_at: @last_seen_at) %>

    <%- if @featured_topics.present? %>
      <h3><%=t 'user_notifications.digest.top_topics' %></h3>

      <%- @featured_topics.each_with_index do |t, i| %>
        <%= link_to t.title, "#{Discourse.base_url}#{t.relative_url}" %>

        <%- if t.best_post.present? %>
          <div class='digest-post'>
            <%= email_excerpt(t.best_post.cooked) %>
          </div>
        <%- end %>

        <%- if i < @featured_topics.size - 1 %><hr><% end %>

      <%- end %>
    <%- end %>

    <%- if @new_topics.present? %>
      <h3><%=t 'user_notifications.digest.other_new_topics' %></h3>

      <%- @new_topics.each do |t| %>
        <ul>
          <li>
            <%= link_to t.title, "#{Discourse.base_url}#{t.relative_url}" %>

            <span class='post-count'><%= t('user_notifications.digest.posts', count: t.posts_count) %></span>

            <%- if t.category %><span style='background-color: #<%= t.category.color %>; color: #<%= t.category.text_color %>; font-size: 12px; padding: 4px 6px; font-weight: bold'><%= t.category.name %></span><%- end %>
          </li>
        </ul>
      <%- end -%>

    <%- end -%>

  <span class='footer-notice'>
    <%=raw(t :'user_notifications.digest.unsubscribe',
       site_link: html_site_link,
       unsubscribe_link: link_to(t('user_notifications.digest.click_here'), email_unsubscribe_path(host: Discourse.base_url, key: @user.temporary_key, only_path: false)))  %>
  </span>
  </td>
</tr>
</table>