The best term is actually girl. Alternative words include sis and sister. I’ve also heard girlfriend though that’s more common among older people (~late 20s to 30s as opposed to teens and college-aged people).
“That’s not cool, man” → “That’s not cool sis.”
“Dude, look at this!” → “Girl, look at this!”
“Hey, calm down, bro” → “Sister. Calm down.”
Which words should be used and where in a sentence (and if they take a comma, double comma, period, or no punctuation at all) involves a lot of subtlety; it’s probably idiomatic. For example, don’t say
“Girlfriend, that’s not cool.”
“Look at this(,) girl!”†
“Hey, sis, calm down!”
Since you’re asking this question I will assume you’re not a “native” speaker, so I’d avoid trying to imitate it in your writing.
Keep in mind that, just like dude, bro, etc are mainly used among groups of guys and their close female friends, girl, sis, etc are mainly used among groups of girls and their close male friends. Setting matters too. I wouldn’t imagine you’d use any of these terms in say, the workplace, regardless of who you’re talking to.
I can’t really think of any popular examples of specific cross-terms that a guy would use to address a girl or vice-versa. This is probably because men tend to hang out with other men and women tend to hang out with other women, so cross-terms have never really had a chance to develop. In my experience, people will use whatever set of words corresponds to the majority in the friend group, and use them to address everyone in the group, regardless of gender.
Also, although this isn’t exactly an answer, you can sidestep the issue by replacing the gendered terms with something like “yo” which sounds just as natural and casual.
“That’s not cool, man” → “Yo that ain’t cool.”
“Dude, look at this!” → “Yo, look at this!”
“Hey, calm down, bro” → “Yo. Calm down.”
Yo is only appropriate if you’re trying to address them and get their attention at the same time though. If you want to say something like “girl/bro lay off, I’ve had a real tough day,” you need the gendered terms.
† This can instead mean “I can’t believe this <
person I don’t like> is actually doing that right now!!” if you omit the comma (for example if you’re texting) so most people put “girl” at the front to avoid that ambiguity and it spills back over into spoken language.