When 还 is used before an adjective, it means “passably, fairly”.
他还好。
He is fairly well.
教室不大，但还明亮。
The classroom is not big, but it is fairly bright.
屋子不大， 收拾得倒还干净。
The room is small，but it’s kept quite tidy.
This rope is fairly strong.
这根绳子还算结实。