Getting Lists to Stack

Hello,

I have installed your plugin on my front page at http://www.unconventionallife.net. I modified the CSS to have the lists and thumbnails display horizontally, using float: left. I have three separate instances of your plugin each with a different filter.

My question is this: I would like each separate list to stack vertically when I shrink the screen horizontally. Currently, each li shrinks horizontally until it is so narrow and squished as to be un-readable for someone using a smartphone.

Can you suggest some code to allow me to do this?

Thanks
Russ

http://ww.wp.xz.cn/plugins/recent-posts-plus/