How to have background images in slideshows

Hello,

I created an image slideshow using bootstrap carousel. Images do not look right. I would like to apply css to images like this: background-size: cover; so I hope images will look better.

views setting

When I inspect my slideshow image, I see this:

note that element style is blank.

element.style {
}
css_injector_5.css?oomolo:1
.carousel-inner > .item > img, .carousel-inner > .item > a > img {
    line-height: 1;
    width: 100%;
}

However, I inspected a site and I noticed that element.style has background image.

element.style {
    background-image: url(http:...large.jpg);
}
__maindomain-ww……_-0,topc…:387
.iosSlider .slider .item .img-bg {
    height: 100%;
    background-size: cover;
    background-position: center top;
    background-repeat: no-repeat;
}

How can I create my slideshows so I can apply css to images like this background-size: cover;?

Thanks.