css3动画怎么使圆形旋转

<div class="demo"></div><style>
    .demo {
        width: 250px;
        height: 250px;
        border: 50px solid red;
        border-left-color: blue;
        border-right-color: yellow;
        border-top-color: #04f105;
        margin: 100px;
        border-radius: 50%;
        animation: circle 2s infinite linear;
    }
    @keyframes circle {
        0% {
            transform: rotate(0deg);
        }

        100% {
            transform: rotate(-360deg);
        }
    }</style>

<div class="demoout">
    <div class="demo"></div></div><style>
    body {
        background: black;
    }

    .demo {
        width: 250px;
        height: 250px;
        border: 3px solid white;
        border-left-color: blue;
        border-right-color: yellow;
        margin: 25px;
        border-radius: 50%;
        animation: circle 4s infinite ease;
        background: white;
    }

    .demoout {
        width: 300px;
        height: 300px;
        border: 3px solid white;
        border-top-color: green;
        border-bottom-color: red;
        margin: 100px;
        border-radius: 50%;
        animation: circle 4s infinite linear;
        background: white;
    }

    @-webkit-keyframes circle {
        0% {
            transform: rotate(0deg);
        }

        100% {
            transform: rotate(-360deg);
        }
    }</style>