html {
  --s:67px; /* shape size */
  --m:4px;  /* line thickness */

  --v1: #fff 119.5deg, #0000 120.5deg;
  --v2: #000  119.5deg, #0000 120.5deg;
  background:
    conic-gradient(at var(--m)              calc(var(--s)*0.5777), transparent 270deg, #000 0deg),
    conic-gradient(at calc(100% - var(--m)) calc(var(--s)*0.5777), #000 90deg,  transparent 0deg),
    conic-gradient(from -60deg at 50% calc(var(--s)*0.8662)             , var(--v1)),
    conic-gradient(from -60deg at 50% calc(var(--s)*0.8662 + 2*var(--m)), var(--v2)),
    conic-gradient(from 120deg at 50% calc(var(--s)*1.4435 + 3*var(--m)), var(--v1)),
    conic-gradient(from 120deg at 50% calc(var(--s)*1.4435 +   var(--m)), var(--v2)),
    linear-gradient(90deg, #fff calc(50% - var(--m)),#000 0 calc(50% + var(--m)), #fff 0);
  background-size: calc(var(--s) + 2*var(--m)) calc(var(--s)*1.732 + 3*var(--m)); 
  mix-blend-mode:lighten;
}
html:before {
  content: "";
  position: absolute;
  inset: 0;
  background:linear-gradient(90deg,red,blue,green) left/400% 100%;
  animation:f 2s infinite alternate linear;
}

@keyframes f {
  100% {background-position:right}
}

External CSS

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