This is the 9230th most frequent Russian word.
советская
"Soviet" or "pertaining to the Soviet Union."
Here, 'советское' refers to the 'Soviet' era or time period, being an adjective associated with 'время' (time).
В советское время многое было иначе.
In Soviet times, many things were different.
'советском' modifies 'стиле' (style), indicating a connection to or characteristic of the Soviet design.
Эти здания построены в советском стиле.
These buildings are built in the Soviet style.
'советской' here describes 'культуре' (culture) as belonging or related to the Soviet Union.