Improve chosen multi-select style

Chosen single-select has been styled to match this theme but the chosen multi-select boxes are not.
The multi-select boxes have a different border color, a gradient in the background, the selected options have a gradient background and the drop-down has a shadow. In both single and multi-select drop-downs, the "highlighted" item has a gradient.

Here is what chosen select boxes look like currently.

I have modified the style to fix these issues. I removed the gradients, fixed the border color on the muti-select, made the highlighted item color match border color, removed the box-shadow, and removed the gradient and border on the multi-select selected options.
Here is what they look like after this patch.