.slide:first-of-type {
background-image: url("https://www.bmw.pl/content/dam/bmw/common/home/teaser/BMW-5series-sedan-home-teaser-s2-XXL-desktop.jpg/jcr:content/renditions/cq5dam.resized.img.1680.large.time1476370052435.jpg");
}
.slide:nth-of-type(2) {
background-image: url("https://images.pexels.com/photos/288477/pexels-photo-288477.jpeg?w=1260&h=750&auto=compress&cs=tinysrgb");
}
.slide:last-of-type {
background-image: url("https://images.pexels.com/photos/27665/pexels-photo-27665.jpg?w=1260&h=750&auto=compress&cs=tinysrgb");
}
tu masz 3 element, w których zmieniasz obrazki
to tu masz problem?
bo ja sobie wstawiłam to http://viamoto.info/wp-content/uploads/2017/01/8.jpg i śmiga