Maybe the Wordpress css has a css rule that overrides yours. Keep in mind that if the theme css have eg. this css rule:
.paragraph p{
text-align: left;
}
and below that you add this rule:
p{
text-align: right;
}
Even if you put your rule as the last one, it has lesser priority than the theme one so the css rule applied will be the theme one. Try to add the modifier important! so you'll have:
p{
text-align: right !important;
}