i don't think i should put id, if i will not put id it will effect all the forums.

What are you talking about?, look it would be best if you either posted your template code complete with the code added so we can see what you have done or just abandon this thread.

<li class="forumbit_nopost {vb:raw forum.statusicon} L1" id="cat{vb:raw forum.forumid}">
<div class="forumhead foruminfo L1 collapse">
<h2>
<span class="forumtitle"><a href="{vb:link forum, {vb:raw forum}}">{vb:raw forum.title}</a></span>
<span class="forumlastpost">{vb:rawphrase last_post}</span>
<vb:if condition="!$show['collapsable_forums']">
<a class="collapse" id="collapse_c_cat{vb:raw forum.forumid}" href="{vb:raw relpath}#top"><img src="{vb:stylevar imgdir_button}/collapse_40b.png" alt="" title="{vb:rawphrase collapse_this_category}" /></a>
</vb:if>
</h2>

<vb:if condition="$show['forumdescription'] OR $show['subforums']">
<div class="forumrowdata">
<vb:if condition="$show['forumdescription']"><p class="subforumdescription">{vb:raw forum.description}</p></vb:if>

<vb:if condition="$show['subforums']">
<div class="subforums">
<h4 class="subforumlistlabel">{vb:rawphrase subforums}:</h4>
<ol class="subforumlist commalist">
{vb:raw forum.subforums}
</ol>
</div>
</vb:if>
</div>
</vb:if>
</div>
<vb:if condition="$childforumbits">
<ol id="c_cat{vb:raw forum.forumid}" class="childforum">
{vb:raw childforumbits}
</ol>
</vb:if>
</li>