Edit in JSFiddle

@keyframes rotate { /* CSS3 standard */
    0% {
        transform: rotate(0deg);
    }
    25%  {
        transform: rotate(90deg);
    }
    50%  {
        transform: rotate(180deg);
    }
    75% {
        transform: rotate(270deg);
    }
    100% {
        transform: rotate(360deg);
    }
}
 
@-moz-keyframes rotate { /* Firefox */
    0% {
        -moz-transform: rotate(0deg);
    }
    25%  {
        -moz-transform: rotate(90deg);
    }
    50%  {
        -moz-transform: rotate(180deg);
    }
    75% {
        -moz-transform: rotate(270deg);
    }
    100% {
        -moz-transform: rotate(360deg);
    }
}
 
@-webkit-keyframes rotate { /* Safari and Chrome */
    0% {
        -webkit-transform: rotate(0deg);
    }
    25%  {
        -webkit-transform: rotate(90deg);
    }
    50%  {
        -webkit-transform: rotate(180deg);
    }
    75% {
        -webkit-transform: rotate(270deg);
    }
    100% {
        -webkit-transform: rotate(360deg);
    }
}
 
@-o-keyframes rotate {  /* Opera */
    0% {
        -o-transform: rotate(0deg);
    }
    25%  {
        -o-transform: rotate(90deg);
    }
    50%  {
        -o-transform: rotate(180deg);
    }
    75% {
        -o-transform: rotate(270deg);
    }
    100% {
        -o-transform: rotate(360deg);
    }
}
 
p.rotate {
    background:#268bd2;
    width:40px;
    height:40px;
    border-radius:4px;
    margin: 20px auto;
    animation: rotate 3s forwards infinite; /* CSS3 standard */
    -moz-animation: rotate 3s forwards infinite; /* Firefox */
    -webkit-animation: rotate 3s forwards infinite; /* Safari and Chrome */
    -o-animation: rotate 3s forwards infinite; /* Opera */
}

<p class="rotate"></p>