使用jQuery动画向左滑动时保留css float

I am having css issues when using jQuery's animate. I have tried a few methods to get this working but to no avail. Basically all I'm trying to do is have a side bar slide left and right via a click event but it seems the css (float) is causing issues. I know exactly the problem but not sure how to exactly fix it. Rather than me trying to explain the problem i have reproduced it with jsfiddle: I am having css issues when using jQuery's anim