How to make sidebar shrink and collapse?
 

I have examples of two separate websites, running on two different Wordpress themes. I would like the sidebar on >EDIT< shrink and collapse, just the way it behaves at >EDIT<.

It gets narrower, and when it collapses, the content on the left hand side gets the entire width of the screen. Can somebody tell me how to do that?

Thank you.

# # # EDIT

Are @media queries the only way to achieve this effect. I dont like the sidebar getting to thin, it does not look good.

# # # EDIT2

@media queries are the only way to do that, I think.

Thank you.