This is the 3885th most frequent Japanese word.
カラ
"カラ" can mean "empty," "shell," or "husk," depending on context.
In this sentence, 「から」 is used as a conjunctive particle meaning "because," connecting the reason (blue sky) with the result (bright mood).
空は青いから気分も晴れる。
The sky is blue, so it brightens the mood.
Here, 「から」 serves as a postpositional particle indicating the starting point or origin, in this case referring to the viewpoint from the room.
部屋から外の風景がよく見える。
You can see the view outside well from the room.
「から」 in this context again acts as a conjunctive particle meaning "because," expressing a causal relationship between past rain and the action of bringing an umbrella.