使光滑图像滑块始终覆盖为背景

I am using Slick as a full width background slider. I just want a slideshow that is covering the whole background. My problem here is that the images seems to only adjust automatically to the width of the page. This means that if the browser gets too narrow, the image will not cover the whole height. I wonder if there is some good way of adjusting the image size to always cover the background. I want the image to either overflow horizontally or vertically depending on the browsers aspect ratio. as a full width background sli