Famously, the costumes for the first three major solo heroes of the Arrowverse, namely Green Arrow, Flash and Supergirl, were all designed by 12-time Academy Award-nominated (and four-time Academy Award-winning) costume designer, Colleen Atwood. Atwood did a wonderful job with Arrow and Flash, but she probably got the most attention
for her work on Melissa Benoist's Supergirl costume. Atwood put so much attention into the design that she specifically had Benoist lay on a bench during a fitting so that Atwood could see what it would look like in flight.
Interestingly, though, Atwood specifically noted about Supergirl's bare legs, "I feel like there’s a real love for Americana with Supergirl, and I wanted to really embrace that heart of women — there’s enough skin out there in the world, it’s not for everybody and Melissa was just the right person to pull it off." While that is a fine sentiment, the initial design for Supergirl by Atwood seemingly does show a decent amount of Supergirl's bare legs. In the final costume, that is all covered in shaded tights. The reaction to the costume would have certainly been a lot different had Supergirl's legs not been covered in the final costume.