It doesn't matter what; anything is fine — a casual expression used when you have no particular preference.
夕食は何でもいいよ。あなたの食べたいものにしよう。
I don't mind what we have for dinner. Let's have what you want to eat.
映画を選ぶのはあなたに任せる。何でもいい。
I'll leave the movie choice to you. Anything is fine.
プレゼントは何でもいいと言われると逆に困る。
Being told 'anything is fine' about a gift actually makes it harder.
会議の時間は何でもいいが、できれば午前中が助かる。
Any time for the meeting is fine, but morning would be preferable if possible.