I'm using flexbox to responsively lay out of a bunch of images.
height: 100%, which limits the container to a fixed height, use
min-height: 100% or remove height altogether.
height property is installed properly, you may need to apply the
min-height to parent or ancestor elements.
Additional notes from OP:
Add the height to the direct children of the flex-box, this allows the container to determine its height.
On another note, if you put the height on the sub-children (not direct descendants), the container flex-box will not know how to set its own size and will have no height.