openproject/app/views/mailer/_border_table.html.erb

<table <%= placeholder_table_styles(width:'100%',style: "width:100%;border-width:1px;border-color:#E0E0E0;border-style:solid;border-radius:10px") %>>
  <tr>
    <%= placeholder_cell('12px', vertical: false) %>
  </tr>
  <tr>
    <td>
      <table <%= placeholder_table_styles(width:'100%',style: 'width:100%;font-size:14px;') %>>
        <%= yield %>
      </table>
    </td>
  </tr>
  <tr>
    <%= placeholder_cell('12px', vertical: false) %>
  </tr>
</table>

<table>
  <tr>
    <%= placeholder_cell('20px', vertical: false) %>
  </tr>
</table>