CSS changes needed to apply to one form only - Joomla! Forum - community, help and support

apologies in advance newbie questions follow.

we have form uses template called div_div. 
do use 'edit css style' button under form description apply style form or go default template in template manager site (which ddcleanashy) , edit css there? 
i think need use edit css style button within form, change write distinct css form? 
the manual says create new css file named [formid].css. 
where create new css file within joomla interface?
and, lastly, how div_div template relate ddcleanashy template?

tia,

jej1216

ok, little smarter when first posted this.  have created css file in com_fabrik\css , named 23.css since form labelled 23.

following fabrik user manual chapter on css files created file 23.css following entries (copied manual):

.fabriklabel{
width:30%
float:left;
}

.fabrikerror{
color:red;
}

.elementerrorhighlight{
background:red;
}
.input:focus, textarea:focus{
background-color #e1f1c2;
{

i save file, when open form, fields displayed before - no change.

also, when in com_fabrik\css there no existing css files.

help!