JQuery动画边框没有移动div

I want to animate a div by first making it's border thicker by 5px on mouseenter, then decreasing the border by 5px on mouseleave, the tricky part is that I don't want the div to look like it's moving (if you just animate the borders, the whole div will look like it shifts, not just the border getting thicker/thinner). I'm very close, but I'm stuck on the last part: mouseleave. What I have so far is:I want to animate a div by first making it's bo