This phrase means "It's a night where anything goes" or "It's a whatever kind of night" in English. It has a casual, somewhat indifferent tone about the night.
- どうでもいい (dou demo ii): "whatever," "doesn't matter," "I don't care"
- よな (yo na): a sentence-ending particle adding emphasis and seeking agreement
- 夜 (yoru): night
- だけど (dakedo): but, although
So, it expresses a mood where the speaker feels indifferent or nonchalant about the night.
