How to make a grid on flexes, in which one column was enclosed in a background?

Question

css

There is a board design (I attach a screen).
The left column (sidebar) differs from all other columns in that it has a white background, but the content of this white background is equal to each of the 5 columns.
How can this be done in flex?
PS. I'm a beginner coder, a very big request to explain in a language understandable to the lamer :)

Answer 1

Somehow like that? https://codepen.io/elijah_tr/pen/veryxv
(Chrome, Firefox, IE11, Edge, and even rubber)