<main>
  <svg class="ip" viewBox="0 0 256 128" width="256px" height="128px" xmlns="http://www.w3.org/2000/svg">
    <defs>
      <linearGradient id="grad1" x1="0" y1="0" x2="1" y2="0">
        <stop offset="0%" stop-color="#5ebd3e" />
        <stop offset="33%" stop-color="#ffb900" />
        <stop offset="67%" stop-color="#f78200" />
        <stop offset="100%" stop-color="#e23838" />
      </linearGradient>
      <linearGradient id="grad2" x1="1" y1="0" x2="0" y2="0">
        <stop offset="0%" stop-color="#e23838" />
        <stop offset="33%" stop-color="#973999" />
        <stop offset="67%" stop-color="#009cdf" />
        <stop offset="100%" stop-color="#5ebd3e" />
      </linearGradient>
    </defs>
    <g fill="none" stroke-linecap="round" stroke-width="16">
      <g class="ip__track" stroke="#ddd">
        <path d="M8,64s0-56,60-56,60,112,120,112,60-56,60-56"/>
        <path d="M248,64s0-56-60-56-60,112-120,112S8,64,8,64"/>
      </g>
      <g stroke-dasharray="180 656">
        <path class="ip__worm1" stroke="url(#grad1)" stroke-dashoffset="0" d="M8,64s0-56,60-56,60,112,120,112,60-56,60-56"/>
        <path class="ip__worm2" stroke="url(#grad2)" stroke-dashoffset="358" d="M248,64s0-56-60-56-60,112-120,112S8,64,8,64"/>
      </g>
    </g>
  </svg>
</main>

* {
  border: 0;
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
:root {
  --hue: 223;
  --bg: hsl(var(--hue),90%,95%);
  --fg: hsl(var(--hue),90%,5%);
  --trans-dur: 0.3s;
  font-size: calc(16px + (24 - 16) * (100vw - 320px) / (1280 - 320));
}
body {
  background-color: var(--bg);
  color: var(--fg);
  font: 1em/1.5 sans-serif;
  height: 100vh;
  display: grid;
  place-items: center;
  transition: background-color var(--trans-dur);
}
main {
  padding: 1.5em 0;
}
.ip {
  width: 16em;
  height: 8em;
}
.ip__track {
  stroke: hsl(var(--hue),90%,90%);
  transition: stroke var(--trans-dur);
}
.ip__worm1,
.ip__worm2 {
  animation: worm1 2s linear infinite;
}
.ip__worm2 {
  animation-name: worm2;
}

/* Dark theme */
@media (prefers-color-scheme: dark) {
  :root {
    --bg: hsl(var(--hue),90%,5%);
    --fg: hsl(var(--hue),90%,95%);
  }
  .ip__track {
    stroke: hsl(var(--hue),90%,15%);
  }
}

/* Animation */
@keyframes worm1 {
  from {
    stroke-dashoffset: 0;
  }
  50% {
    animation-timing-function: steps(1);
    stroke-dashoffset: -358;
  }
  50.01% {
    animation-timing-function: linear;
    stroke-dashoffset: 358;
  }
  to {
    stroke-dashoffset: 0;
  }
}
@keyframes worm2 {
  from {
    stroke-dashoffset: 358;
  }
  50% {
    stroke-dashoffset: 0;
  }
  to {
    stroke-dashoffset: -358;
  }
}