This is the 7127th most frequent Spanish word.
feliz
Happy.
In this sentence, 'feliz' is used as an adjective to describe the speaker's emotional state.
Estoy muy feliz por tu éxito.
I am very happy for your success.
Here, 'feliz' modifies 'rostro' (face) to describe its appearance showing happiness.
El niño tenía un rostro feliz mientras jugaba.
The child had a happy face while playing.
In this case, 'feliz' describes the overall positive experience of the weekend.