The whole of the blue square isn't filled in though.

We can see that a quarter of two circle are in the way and since they are the same size I will assume it's half of one circle:

This area will beLeave it in this form to avoid rounding errors

The area of the small square is but since half of it is taken by the blue triangle we can do

Now we can take the sum of these from the big square which has an area of