Resize t3-sidebar??

Hello,

i've a quetstion about the class t3-sidebar.
If I resize the t3-sidebar smaller, what must i do, that the t3-content becomes the same size bigger.
In my Site I've resize the t3-sidebar and after that I had an column between t3-sidebar and t3-content (look at the picture).

Have anybody an idea?

Thank you very much and best regards...

Sascha