Merry meet @angel4,
That’s a great question!
I’m not quite sure which definition of positive you are looking for, so I hope you don’t mind if I offer up my thoughts on both!
(Apologies in advance, as this great question kickstarted my love for magickal theory 
)
[When Positive = Good and Negative = Bad]
From an ethical perspective (with positive being good and negative being bad as a human would define them) I would agree with Crystal and Marsha- I would say that, in general, the Elements are depicted and perceived as generally positive.
That being said, they are forces of nature, which can be just as cruel as it is kind- the ocean that is gentle and calm on a sunny day can be a raging storm that destroys the coast the next. It’s hard to apply human ethics to non-human things, so in this sense, I might actually describe the elements as being neutral- neither good nor evil. Like tools, they can be used in alignment of the person wielding them.
[When Positive = Yang and Negative = Yin]
Positive and negative are opposite traits, so, like most opposite traits (hot and cold, hard and soft, light and dark, etc) they are sorted into categories.
In this sense, Fire and Air are often associated with the Divine Masculine or Yang energies. This type of energy is associated with the “positive” trait 
Water and Earth are often associated with the Divine Feminine or Yin energies. This type of energy is associated with the “negative” trait (not necessarily negative as in evil, but negative as in negative space- empty, open) 
Spirit, as the only non-material element, would not be associated with physical categorizations (in my opinion) and would then be inherently neutral 
These are just my thoughts about it, offered up in hope of helping you make your own decisions about the alignments of the elements! Thank you again for such a great question! 
Blessed be!