How to make a two column drop down list on flexbox?

Question

css

Everything seems to work, but there is a nuance, the drop-down list takes only half the width of the columns
codepen.io/lemme/pen/LZVPYm
How to make the width of the drop-down list (.navigation__items_dropdown) = the width of the children (including columns). Currently, it only takes up half the width of the first column.
UPD
https://wireframe.cc/8amMKC

Answer 1

codepen.io/anon/pen/bedGLa
Nothing will work without manually setting the width for the container. This problem is only with flex-direction: column.
stackoverflow.com/questions/33891709/when-flexbox-...
If you set the width, then everything will be ok:
codepen.io/anon/pen/XKbbZZ
Among the adequate solutions, only width calculation with jQuery is offered