Replace the separate button by an onCLick event on the @

This works around the styling issue.

interface/web/mail/templates/mail_user_mailbox_edit.htm

@@ -7,13 +7,10 @@
                 <div class="col-sm-9">
 				    <div class='input-group'>
 						<input type="text" id="email_local_part" name="email_local_part" value="{tmpl_var name='email_local_part'}" class="form-control" />
-						<span class='input-group-addon'>@</span>
+						<span class='input-group-addon input-group-field' onClick="javascript: navigator.clipboard.writeText(document.getElementById('email_local_part').value + '@' + document.getElementById('email_domain').value);" title="{tmpl_var name='copy_to_clipboard_txt'}">@</span>
                         <div class='input-group-field'>
 							<select name="email_domain" id="email_domain" class="form-control" style="height:50px;min-width:170px;">{tmpl_var name='email_domain'}</select>
                         </div>
-                        <a class="btn btn-default formbutton-narrow" href="javascript: navigator.clipboard.writeText(document.getElementById('email_local_part').value + '@' + document.getElementById('email_domain').value);" title="{tmpl_var name='copy_to_clipboard_txt'}">
-                            <span class="fa fa-clone"></span>
-                        </a>
                     </div>
 				</div>
             </div>