Questions & Answers about Este dia é especial.
Because dia is a masculine noun.
Portuguese demonstratives must agree with the noun in gender and number:
- este = masculine singular
- esta = feminine singular
- estes = masculine plural
- estas = feminine plural
So:
- este dia = this day
- esta noite = this night
Even though dia ends in -a, it is still masculine. That is one of the exceptions learners have to memorize.