There isn’t any space to distribute. You have set the flex-basis and width in a way that doesn’t allow for 7 elements to sit side by side and have any space between them.
To see the space you would have to set the flex-basis/width to 14% and below (100 / 7 = 14,285) or some fixed value small enough (that is if you set box-sizing: border-box otherwise you have to account for the border size as well). The space will also disappear as the container shrinks down.
Just as an aside. There is no point in having 6 classes with the same styles. The point of a class is that the styles can be shared on different elements using the same class.