This is the 5427th most frequent Swedish word.
feliz
"Feliz" is not Swedish; it is Spanish and means "happy" in English.
The word 'feliz' is used here as an adjective to express a state of happiness or joy experienced by a person.
Han känner sig så feliz idag.
He feels so happy today.
'Feliz' is employed as an adjective comparing the joyful nature of her smile and her eyes.
Hennes leende var lika feliz som hennes ögon.
Her smile was as joyful as her eyes.
In this instance, 'feliz' functions as an adjective describing the happy nature of the moment they shared.