In running the below MWE R Shiny code the sidebar panel width correctly remains fixed while the main panel expands as the user expands the size of the window. When the user increases the window size, the size of the plot also increases which is correct. However, when the user decreases the size of the window after having increased it, the plot size does not readjust to the smaller window size: the plot size remains the same large size it was when the window size was increased. How can the plot size be readjusted when the user reduces the window size? While maintaining the same fixed-width sidebar panel.

The MWE code shown below works exactly as I would like, where the sidebar panel width remains fixed while the main panel expands as the user manually increases the size of the window. Instead of the UI structure I use in the below code, is it possible to do the same thing but instead using the following UI structure with CSS to fix the width of the sidebar panel? The below UI structure is better in my case because would be much easier to integrate into my larger code:

This is my code:

Considering following argonDash app: