This kind of music is my jam.

A popular hit that's semi-recent...well I guess not anymore is "Pumped Up Kicks" which was about a school shooting but was written with this carefree tone that really makes it all the more deranged.

There's a band I listen to called HIM and they have a dancy 80s rock vibe mixed in with gothic music tones. Their shtick lyrically is playing with goth romance cliches so you get a lot of "I'll love you to death" kind of stuff. Other Finnish rock bands that were around in the early 2k have similar stuff (69 Eyes, The Rasmus, Negative) but it varies whether or not it hits what you're looking for.

I, personally, think a lot of post-grunge music does this as well. So Cold by Breaking Benjamin, Saferwaters by Chevelle, Deftones plays around with this quite a bit as well (I know they're nu metal but whatever subgenres are nuts).

You'll find it littered throughout a lot of other rock music as well but that's mainly a consequence of it having dark lyrics while trying to have a type of dancy vibe for commercial viability. I think the more esoteric you get in rock the more this goes away. Prog rock seems to be a good vein for this kind of stuff too (Tool, Pink Floyd, Rush) but they tend to flip through a lot of themes so it's hard to condense a single song into "happy but sad" in the specific way you're seeking.

Back to more pop stuff - Save Your Tears by The Weeknd is a good one. Maneskin's cover of Beggin' I feel does this as well.