display: inline-block; width: 10px; min-height: 2px;
            padding-right: 2px;
            border-left: 2px solid currentColor; border-right: 2px solid currentColor;  
            background-color: currentColor; background-clip: content-box;
            box-sizing: border-box;
            -webkit-animation: dot 4s infinite step-start both;
            _zoom: expression(this.innerHTML = '...'); /_ IE7 _/
        }
        .dotting:before { content: '...'; } /_ IE8 _/
        .dotting::before { content: ''; }
        :root .dotting { margin-left: 2px; padding-left: 2px; } /_ IE9+ */

@-webkit-keyframes dot {
    25% { border-color: transparent; background-color: transparent; }          /* 0个点 */
    50% { border-right-color: transparent; background-color: transparent; }    /* 1个点 */
    75% { border-right-color: transparent; }                                   /* 2个点 */
}```