Category and Archive box

Hi Peeps!

I’ve included the Category and the Archive in my sidebar. I’ve also selected the “drop down” menu option, so both appears with a little box in the sidebar.
However, the box becomes bigger (wider) as the category names become longer. If the name is too long, the category box will go outside of the sidebar making it look very unprofessional.

Is there a way for format the box so that it stays the same width no matter how long the category name is?
I would really like to have both the Category and Archive box have the same width.

Thanks!