This was one of Millie Bobby Brown's looks for Late Night with Stephen Colbert. It looks like a fun and comfortable outfit for late night shenanigans at the Colbert show. The big heart is a nice, vibrant touch to this otherwise simple outfit.
Stranger Things Fact Number Eighteen: The Duffer brothers played a very horrible prank on Noah Schnapp's mother (he's the actor who plays Will) while on set for season 1. You may remember that there is a fake Will's dead body in the show. You might already be piecing together the prank. They scared the hell out of his mom with the fake body by hanging it in a closet for her to find. My mom would have killed them for that. Then she would have killed me for letting them do that. Moms are weird.