Complex sentence: By the beginning of the 21st century it had altered into what is known today as'street fashion', a term used to describe fashion in which the wearer customizes outfits by adopting a mixture of current and traditional trends.
Split into simpler sentences: By the beginning of the 21st century it had altered into what is known today as'street fashion'. The term'street fashion' is used to describe fashion where the wearer customizes outfits by adopting a mixture of current and traditional trends.