CSS만으로 (제출중인 Ajax 양식) 버튼에 빙글빙글을 표시하는 예

.submit.loading::before {
    background-color: rgba(0,0,0,.5);
    content: "";
    display: block;
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    width: 100%;
}
.submit.loading::after {
    animation: rotate 1s infinite linear;
    content: "*";
    color: #fff;
    height: 100%;
    left: 0;
    position: absolute;
    top: 0;
    width: 100%;
}
@keyframes rotate {
    0% { transform: rotate(0); }
    100% { transform: rotate(360deg); }
}