Пример

Код

HTML

<div class="hourglass"></div>

CSS

* {
    border: 0;
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
:root {
    --bg: #e3e4e8;
    --fg: #2e3138;
    --primary: #255ff4;
    font-size: calc(16px + (24 - 16) * (100vw - 320px) / (1280 - 320));
}
body {
    background: var(--bg);
    display: grid;
    font: 1em/1.5 sans-serif;
    height: 100vh;
    place-items: center;
}

.hourglass, .hourglass:before, .hourglass:after {
    animation-duration: 4s;
    animation-iteration-count: infinite;
}
.hourglass {
    --polygonH: polygon(0% 0%,100% 0%,100% 5.55%,95% 5.55%,95% 28%,60% 46%,60% 54%,95% 72%,95% 94.45%,100% 94.45%,100% 100%,0% 100%,0% 94.45%,5% 94.45%,5% 72%,40% 54%,40% 46%,5% 28%,5% 5.55%,0% 5.55%);
    animation-name: flip;
    animation-timing-function: ease-in-out;
    background-image: linear-gradient(var(--primary) 0.5em,#737a8c55 0.5em 8.5em,var(--primary) 8.5em);
    clip-path: var(--polygonH);
    -webkit-clip-path: var(--polygonH);
    overflow: hidden;
    position: relative;
    width: 5em;
    height: 9em;
    z-index: 0;
}
.hourglass:before, .hourglass:after {
    animation-timing-function: linear;
    content: "";
    display: block;
    position: absolute;
}
.hourglass:before {
    --polygonB1: polygon(0% 0%,100% 0%,100% 24%,50% 47%,50% 47%,50% 47%,50% 47%,50% 47%,50% 47%,50% 47%,50% 47%,0% 24%);
    --polygonB2: polygon(0% 4%,100% 4%,100% 24%,55% 45%,55% 100%,55% 100%,55% 100%,45% 100%,45% 100%,45% 100%,45% 45%,0% 24%);
    --polygonB3: polygon(0% 24%,100% 24%,100% 24%,55% 45%,55% 80%,100% 100%,100% 100%,0% 100%,0% 100%,45% 80%,45% 45%,0% 24%);
    --polygonB4: polygon(45% 45%,55% 45%,55% 45%,55% 45%,55% 58%,100% 76%,100% 100%,0% 100%,0% 76%,45% 58%,45% 45%,45% 45%);
    --polygonB5: polygon(50% 53%,50% 53%,50% 53%,50% 53%,50% 53%,100% 76%,100% 100%,0% 100%,0% 76%,50% 53%,50% 53%,50% 53%);
    animation-name: fill;
    background-color: var(--fg);
    background-size: 100% 3.6em;
    clip-path: var(--polygonB1);
    -webkit-clip-path: var(--polygonB1);
    top: 0.5em;
    left: 0.5em;
    width: 4em;
    height: 8em;
    z-index: 1;
}
.hourglass:after {
    animation-name: glare;
    background:
        linear-gradient(90deg,#0000 0.5em,#0003 0.5em 1.5em,#0000 1.5em 3.5em,#fff3 3.5em 4.5em,#fff0 4.5em 6.5em,#0003 6.5em 7.5em,#0000 7.5em) 0 0 / 100% 0.5em,
        linear-gradient(90deg,#0000 0.75em,#0003 0.75em 1.25em,#0000 1.25em 3.75em,#fff3 3.75em 4.25em,#fff0 4.25em 6.75em,#0003 6.75em 7.25em,#0000 7.25em) 0 0.5em / 100% 8em,
        linear-gradient(90deg,#0000 0.5em,#0003 0.5em 1.5em,#0000 1.5em 3.5em,#fff3 3.5em 4.5em,#fff0 4.5em 6.5em,#0003 6.5em 7.5em,#0000 7.5em) 0 100% / 100% 0.5em;
    background-repeat: repeat-x;
    top: 0;
    left: -3em;
    width: 200%;
    height: 100%;
    z-index: 2;
}
/* Animations */
@keyframes fill {
    from {
        clip-path: var(--polygonB1);
        -webkit-clip-path: var(--polygonB1);
    }
    10% {
        clip-path: var(--polygonB2);
        -webkit-clip-path: var(--polygonB2);
    }
    45% {
        clip-path: var(--polygonB3);
        -webkit-clip-path: var(--polygonB3);
    }
    80% {
        clip-path: var(--polygonB4);
        -webkit-clip-path: var(--polygonB4);
    }
    85%, to {
        clip-path: var(--polygonB5);
        -webkit-clip-path: var(--polygonB5);
    }
}
@keyframes glare {
    from, 90% {
        transform: translateX(0);
    }
    to {
        transform: translateX(3em);
    }
}
@keyframes flip {
    from, 90% {
        transform: rotate(0);
    }
    to {
        transform: rotate(180deg);
    }
}
/* Dark mode */
@media (prefers-color-scheme: dark) {
    :root {
        --bg: #17181c;
        --fg: #c7cad1;
    }
}

Ссылка на codepen