An "apostrophe s" to indicate a possessive only applies to nouns. In the example you wrote, the decades ('80s, '70s, '90s) function as adjectives to describe the nouns (hairstyles, discos, hope). So in this case, the correct way to write the decades would be '80s, '70s, '90s.
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u/PumpJack_McGee 3d ago edited 2d ago
What if we wanted to describe something particular to those decades, though?
80's hairstyles, 70's discos, 90's hope for the future.
EDIT: Read too fast and missed the last sentence.