Scheduled reminders - Email head css attributes are being stripped out
The main issue seems to be the &lt;style&gt; tag defined in the templates. Schedule Reminder uses smarty engine by default which strips down the css styles defined.

This doesn't occur in CiviMail because Smarty is disabled in civicrm.settings.php. If CIVICRM_MAIL_SMARTY is set to 1, civimail will too see this error.

As Smarty processing is done, escape the  tag within {literal}. Something like:

{literal}
  &lt;style&gt;........&lt;/style&gt;
{/literal}
.
.
.
(further html code)


See - http://www.smarty.net/docs/en/language.escaping.tpl.

To avoid the {literal} statements being displayed in the email's wysiwyg view you can enclose those {literal} statements in a &lt;p&gt; tag with class or style to make them hidden - eg &lt;p style="display:none;"&gt;.