In season 1, episode 3 the Super Hero Girl team attempt to save a bakery from destruction (unsuccessfully). At the end of it Batgirl draws the correlation that Lex Luthor is behind it. Supergirl then poses the question, "Lex Luthor is like, the richest man in Metropolis. What could Lex Luthor possibly have against cupcakes?". This is very likely a reference to the internet meme spawned from a children's counting book depicting Lex Luthor stealing 40 cakes, despite being the richest man in Metropolis, thus having no need to steal cakes in the first place.
Kay Hanley, who co-wrote and performed the DC Super Hero Girls theme song, was the lead singer of 90's alternative band Letters to Cleo. Their hit single "Here and Now" was featured during the closing credits of Melrose Place, then a primetime soap opera. The quick-paced singing during the final verse of Super Hero Girls bears similarity to that which is also heard in "Here and Now."
Nicole Sullivan (Supergirl) is exactly 9 years younger than Cathy Cavadini (the voice of Blossom on creator Lauren Faust's husband's show The Powerpuff Girls (1998)) because she was born on April 21, 1970 while Cavadini was born on April 21, 1961. Both actresses voice (small and furry) mammals in television spin-offs of animated films. Cavadini reprises her role as Tanya Mousekewitz (and also voices Yasha Mousekewitz) on Fievel's Adventures in the West (1992) (the television spin-off of An American Tail: Fievel Goes West (1991), the (theatrical) sequel to (the animated film) An American Tail (1986) while Sullivan voices Marlene (the otter) on The Penguins of Madagascar (2008) (the television spin-off of DreamWorks' Madagascar (2005) and it's sequel Madagascar: Escape 2 Africa (2008)). Tanya and Yasha are (both) in An American Tail: Fievel Goes West (1991) (even though Yasha never speaks/babbles/cries in said movie) while Marlene is not in (any of) the movies in the (Madagascar) franchise. Also, there are otters in Finding Dory (2016) (the first Pixar film/sequel that Cavadini does additional voices in)! Also, both Cavadini and Sullivan provide voices in Disney movies from (the year) 2000. Cavadini does additional voices in Dinosaur (2000) while Sullivan voices (Space Ranger) Mira Nova in Buzz Lightyear of Star Command: The Adventure Begins (2000). Also, Cavadini voices Blossom in the video game The Powerpuff Girls: Chemical X-Traction (2001) while Sullivan voices Mira Nova in the video game Buzz Lightyear of Star Command (2000)
This show was released in 2019, the same year of the live action film "Joker."