Динамическая смена фона без перезагрузки и js

 
body {
    margin:0;
    padding:0;
    background: red;
    /* Chrome, Safari, Opera */
    -webkit-animation-name: myfirst;
    -webkit-animation-duration: 15s;
    -webkit-animation-timing-function: linear;
    -webkit-animation-delay: 5s;
    -webkit-animation-iteration-count: infinite;
    -webkit-animation-direction: alternate;
    -webkit-animation-play-state: running;
    /* Standard syntax */
    animation-name: myfirst;
    animation-duration: 15s;
    animation-timing-function: linear;
    animation-delay: 5s;
    animation-iteration-count: infinite;
    animation-direction: alternate;
    animation-play-state: running;
}
 
/* Chrome, Safari, Opera */
@-webkit-keyframes myfirst {
    0%   {background:red;}
    25%  {background:yellow;}
    50%  {background:blue;}
    75%  {background:green;}
    100% {background:red;}
}
 
/* Standard syntax */
@keyframes myfirst {
    0%   {background:red;}
    25%  {background:yellow;}
    50%  {background:blue;}
    75%  {background:green;}
    100% {background:red;}
}