app/views/devise/mailer/confirmation_instructions.html.erb
<h1><%= t('.welcome') %></h1>
<p>
<%= t('.registered') %> <strong><%= @email %></strong>.
<br />
<%= t('.please_confirm') %>
</p>
<hr/>
<p><%= link_to t('confirm_account'), confirmation_url(@resource, :confirmation_token => @token), class: :button %></p>