What's an appropriate reaction to someone coming out?

Hi Gay Redditers! So my sister just came out to me and it was sort of a shock. I'm super happy and proud of her for knowing who she is, but now I'm just sort of speechless. She didn't make a big deal about it, she told me in passing and just said, "Hey! I'm gay!" And I replied with, "Okay! Congratulations" she didn't make a big deal out of it which I'm fine with. My belief has always been love is love, and people shouldn't have to have a big coming out if they don't want to. It's their journey, except because it was so casual and she left right after I replied before letting it sink in, now I have so much in my head and I don't know how to clear it. I just did a lot of research on being gay, using the term gay v. Lesbian and so on so I am as educated as possible on the issue. I have gay friends, and I've had gay teachers and mentors, but with her being in my family this feels different.So I guess my question is was I too casual about her telling me? Have any of you had a similar coming out experience and how did people react? Also, how do I talk to her about it more and bring it up lightly because I have a lot of questions. I want to be as strong an ally as possible so please help!