HTMLify

* {
    box-sizing: border-box;
}

body {
    background-color: #111;
    display: grid;
    place-items: center;
    height: 100vh;
}

.loader {
    width: 32px;
    height: 72px;
    display: inline-block;
    position: relative;
    border: 2px solid #fff;
    animation: fill 2s linear infinite alternate;
    color: #20d0fc;
    border-radius: 0 0 4px 4px;
    transform: perspective(140px) rotateX(-45deg);
}

@keyframes fill {
    0% {
        box-shadow: 0 0 inset;
    }

    100% {
        box-shadow: 0 -70px inset;
    }
}