You'll want to edit the same code you changed before, and just add a new line before the closing bracket (" } ") with the additional attribute.
Old:
p {
padding-bottom:10px;
padding-left: 5px;
padding-right: 5px;
padding-top: 5px;
}
New:
p {
padding-bottom:10px;
padding-left: 5px;
padding-right: 5px;
padding-top: 5px;
text-align:justify;
}
If that was in the template_css file, then that's what you'll need to edit.