app/views/devise/mailer/confirmation_instructions.html.erb
<td style="<%= css_for_mailer_content %>">
<h1 style="<%= css_for_mailer_heading %>">
<%= t("devise_views.mailer.confirmation_instructions.title") %>
</h1>
<p style="<%= css_for_mailer_text %>">
<%= t("devise_views.mailer.confirmation_instructions.welcome") %> <strong><%= @email %></strong>
</p>
<p style="<%= css_for_mailer_text %>">
<%= t("devise_views.mailer.confirmation_instructions.text") %>
</p>
<p style="<%= css_for_mailer_text %>">
<%= link_to t("devise_views.mailer.confirmation_instructions.confirm_link"),
confirmation_url(@resource, confirmation_token: @token),
style: css_for_mailer_link %>
</p>
</td>