how was its style and upgradation?
Its components are officially non-user-replaceable, third parties do sell upgrade kits for the SSDs.
MacBook Air
Although MacBook Air components are officially non-user-replaceable, third parties do sell upgrade kits for the SSDs. 
when did the macbook pro 13 come out 2006 what is this pro? It is the higher-end model of the MacBook family, sitting above the consumer-focused MacBook Air. how reliable is its keyboard? A report by AppleInsider has claimed that the updated butterfly keyboard fails twice as often as previous models, often due to particles stuck beneath the keys. how was the latter mentioned model received? It received mixed reviews which praised its portability, but criticized the compromises made in terms of features.
wiki:8937074
MacBook Air [SEP] Design and upgradability
Although MacBook Air components are officially non-user-replaceable, third parties do sell upgrade kits for the SSDs. The flash memory and battery are enclosed in the casing, and the RAM is soldered onto the motherboard. The flash memory is difficult to access and has a 128 MB cache and a mSATA connection (updated to a proprietary PCIe interface) to the motherboard.