What could be the problem with structure on flexbox?

Question

css

On the codepen, what I need and works ok, but if you uncomment the contents of the blocks, the sidebar immediately flies down, I can’t understand why.

Answer 1

Suggested on another site.
For .list__content
Option 1

width: calc(100% - 200px);
max-width: 76.92308%;

Option 2
width: min-content;