also: どうだってよい
expression, i-adjective (yoi/ii class)
inconsequential; trivial; not worth worrying about
Used to dismiss something as unimportant or not worth concern. Often interchangeable with どうでもいい, but どうだっていい can sound slightly more emphatic or colloquial.
See also: どうでもいい
そんなことはどうだっていい。
That kind of thing doesn't matter.
細かいルールはどうだっていいから、とにかく始めよう。
The detailed rules are trivial, so let's just get started.
expression
whatever; I don't care; whichever
Expresses indifference to a choice or outcome. Can be used as a standalone interjection to show lack of interest.
See also: どうでもいい
A: どっちがいい？ B: どうだっていいよ。
A: Which one do you want? B: I don't care.
彼
Whatever he says, I don't care.
Almost synonymous; どうでもいい is more common and neutral. どうだっていい can feel slightly more emphatic or dismissive.
Phrase composed of どう (how) + だって (even if, no matter) + いい/よい (good). The combination literally means 'no matter how it is, it's fine', giving the sense of indifference.