[abc123]

u'll be wanting

div.myCustomStyle {
blah: something;
}

or

p:first_child div {
blah: #px;
}

but please, don't put tags and words in html in uper case :'(

with first_child div will, obviously, have to be the first child of the "<p>" tags. should work
if not, check out: http://www.w3schools.com/css/