I put this code after class='cPost
{{if $comment->author()->isOnline()}}monline{{else}}moffline{{endif}}
This is the code after my editing
<a id='comment-{$comment->$idField}'></a>
<article {{if $comment->author()->hasHighlightedReplies()}}data-memberGroup="{$comment->author()->member_group_id}" {{endif}} id='elComment_{$comment->$idField}' class='cPost {{if $comment->author()->isOnline()}}monline{{else}}moffline{{endif}} ipsBox ipsResponsive_pull {{if $otherClasses}}{$otherClasses}{{endif}} ipsComment {{if ( settings.reputation_enabled and settings.reputation_highlight and $comment->reactionCount() >= settings.reputation_highlight ) OR $comment->isFeatured()}}ipsComment_popular{{endif}} ipsComment_parent ipsClearfix ipsClear ipsColumns ipsColumns_noSpacing ipsColumns_collapsePhone {{if $comment->author()->hasHighlightedReplies()}}ipsComment_highlighted{{endif}} {{if $comment->isIgnored()}}ipsHide{{endif}} {{if $comment->hidden() OR $item->hidden() === -2}}ipsModerated{{endif}} {{if ( $comment->item()->isSolved() and $comment->item()->mapped('solved_comment_id') == $comment->pid )}}ipsComment_solved{{endif}}'>
{{if $item->isQuestion() and !$comment->new_topic}}
{template="postRating" group="topics" app="forums" params="$item, $comment, $votes"}
{{endif}}
I put this in the custom.css section
article.monline {box-shadow: 0 0 5px 2px rgba(125, 214, 6, 0.31);}