Batman and batgirl

Can I say that they are batman couple? Maybe yes. As we know, although they are from different movie, their costumes are so similar. Many equipments are the same, such as cape, hood, symbol and so on. Of course, the color of superhero costume may be different. But there is a big difference between them, that is the underwear. There is the underwear design on the batman costume which also has the different colors as the other parts of costume. This is very funny, right? Do you know why there isn't the same design on batgirl's costume? Some people will think that batgirl is young and she will feel shy.
However, you can try to design a sexy costume for batgirl according to the batman's costume. This is a meaningful work.