Help turning text backround to flex container

Hey guys I need some help on a flexbox layout im working on. I currently have it set up how I want, however the third column (blue) is not actually a flex container and I need to change that. I ran into a problem with the container expanding too big when I increased the size of the text. I want the text to take up most of the space of this container, so I can’t have it getting bigger when I increase the font size. So I got rid of the last container completely and just put the text in the available space(blue background). This worked to visually express the layout I want but I will need that right (blue) side section to actually be a flex container (but stay same size), so I can give it a different color than the background.

EDIT: placing here because this seems to be where this topic belongs.