upstream-zulip/templates/zerver/emails/email_base_messages.html

{% import 'zerver/emails/email.css' as css_styles %}
<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8" />
        <title>Zulip</title>
        <style>{{css_styles}}</style>
    </head>
    <body>
        {% if has_preheader %}
        <span style="display:none !important;
          visibility:hidden;
          color:transparent;
          mso-hide:all;
          font-size:1px;
          color:hsl(0, 0%, 100%);
          line-height:1px;
          max-height:0px;
          height:0px;
          max-width:0px;
          width:0px;
          opacity:0;
          overflow:hidden;">
            {% block preheader %}{% endblock %}
        </span>
        {% endif %}
        {% block content %}{% endblock %}
        {% block manage_preferences %}{% endblock %}
    </body>
</html>