body{
margin: 0;
Padding: 0;
background: #456585;
}
.slider{
  width: 800px;
height: 400px;
background: url(1.jpg);
margin: 100px auto;
animation: slide 10s infinite;
}
@keyframes slide{
25%{
background: url(2.jpg);
}
50%{
background: url(3.jpg);
}
75%{
background: url(4.jpg);
}
100%{
background: url(1.jpg);
}
}