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

<table <%= placeholder_table_styles(width:'100%',style: "width:100%;min-width:100%") %>>
  <tr>
    <td>
      <table <%= placeholder_table_styles %>>
        <tr>
          <%= placeholder_cell('12px', vertical: true) %>
          <td>
            <table <%= placeholder_table_styles(width:'100%',style: "width:100%") %>>
              <tr>
                <td>
                  <span style="font-size: 24px; color: #333333;">
                    <%= I18n.t(:'mail.salutation', user: @user.firstname) %>
                  </span>
                </td>
              </tr>
              <tr>
                <%= placeholder_cell('8px', vertical: false) %>
              </tr>
              <tr>
                <td>
                  <span style="font-size:16px; color: #1A67A3; font-weight: bold;">
                     <%= summary %>
                  </span>
                </td>
              </tr>
              <tr>
                <%= placeholder_cell('24px', vertical: false) %>
              </tr>
              <tr>
                <td>
                  <%= yield %>
                </td>
              </tr>
              <tr>
                <%= placeholder_cell('40px', vertical: false) %>
              </tr>
            </table>
          </td>
          <%= placeholder_cell('16px', vertical: true) %>
          <td style="vertical-align: top;">
            <table <%= placeholder_table_styles %>>
              <tr>
                <td style="width: 96px; height: 96px;">
                  <%= logo_tag({ alt: "#{Setting.app_title} #{I18n.t(:'mail.logo_alt_text')}", style: "height: 96px;max-width: 240px;"}) %>
                </td>
              </tr>
            </table>
          </td>
        </tr>
      </table>
    </td>
  </tr>
</table>