hydrogen-web/src/ui/web/css/spinner.css

@keyframes spinner {
    0% {
        transform: rotate(0);
        stroke-dasharray: 0 0 10 90;
    }
    45% {
        stroke-dasharray: 0 0 90 10;
    }
    75% {
        stroke-dasharray: 0 50 50 0;
    }
    100% {
        transform: rotate(360deg);
        stroke-dasharray: 10 90 0 0;
    }
}

.spinner circle {
    transform-origin: 50% 50%;
    animation-name: spinner;
    animation-duration: 2s;
    animation-iteration-count: infinite;
    animation-timing-function: linear;
    fill: none;
    stroke: currentcolor;
    stroke-width: 12;
    stroke-linecap: butt;
}

.spinner {
    --size: 20px;
    width: var(--size);
    height: var(--size);
}