/* HTML: <div class="loader"></div> */
.loader {
    display: inline-flex;
    border: 10px solid #000;
    border-radius: 5px;
}

    .loader::before,
    .loader::after {
        content: "0 1 2 3 4 5 6 7 8 9 0";
        font-size: 30px;
        font-family: monospace;
        font-weight: bold;
        line-height: 1em;
        height: 1em;
        width: 1.2ch;
        text-align: center;
        outline: 1px solid #000;
        color: #0000;
        text-shadow: 0 0 0 #000;
        overflow: hidden;
        animation: l4 2s infinite linear;
    }

    .loader::before {
        animation-duration: 4s;
    }

@keyframes l4 {
    100% {
        text-shadow: 0 var(--t,-10em) 0 #000
    }
}