The costume is based on the "modern classic" blue top with red skirt, however it's just poorly designed, poorly made and has the wrong choice of materials. The boots should have stopped below the knees, as per the classic look. The knee covers just look a bit silly.
The boots you're referring to are the thigh high boots Supergirl wore with a minidress following a change in costume:
These worked together, as per the fashions of the day, although didn't last long before the next costume change.
I should mention "Buccaneer" boots are the boots Power Girl wears with her classic costume:
I have an issue with the new costume because it's dull and lifeless... although I will say it could have been worse! Supergirl is my favourite superheroine and I was very disappointed when I saw the costume. It should have been brighter, smoother and most importantly... more feminine! It's just not very flattering.
The designers should have gone with the classic blue dress:
MB would look adorable...